GIFT  OF 
Irs.   Ynes   Ivlexia 


v 


LABORATORY    EXERCISES 

TO  ACCOMPANY 

FIRST    PRINCIPLES    OF    CHEMISTRY 


BY 


RAYMOND  B.   BROWNLEE  ROBERT  W.  FULLER 

STUYVESANT   HIGH    SCHOOL  STUYVESANT    HIGH    SCHOOL 

WILLIAM  J.   HANCOCK  MICHAEL  D.   SOHON 

ERASMUS    HALL   HIGH   SCHOOL  MORRIS    HIGH    SCHOOL 

JESSE   E.  WHITSIT 

DE   WITT   CLINTON    HIGH    SCHOOL 
ALL  OF   NEW  YORK  CITY 


REVISED  EDITION1 


ALLYN    AND    BACON 

Boston  Nefo  gortt  Cjjicago 


B7 


COPYRIGHT,    1908   AND    1917,   BY  RAYMOND   B.    BROWNLEE 
ROBERT  W.    FULLER,  WILLIAM   J.    HANCOCK, 
MICHAEL  D    SOHON,  AND  JESSE    E.  WHITSIT. 


EDI 


PREFACE 

THIS  Laboratory  Manual  is  designed  to  accompany  the  authors' 
"  First  Principles  of  Chemistry."  It  is,  in  some  measure,  founded 
on  Handbook  21  of  the  State  Department  of  Education  of  New 
York,  which  was  prepared  by  the  authors  in  the  spring  of  1905,  and 
which  met  with  such  success  as  to  lead  to  the  writing  of  the  "  First 
Principles  of  Chemistry." 

Such  of  the  experiments  from  the  Handbook  as  appear  in  the 
present  Manual  have  been  carefully  revised  and  improved  where 
experience  has  shown  this  to  be  desirable.  A  number  of  other  ex- 
periments have  been  added  in  order  to  give  greater  freedom  of  selec- 
tion, and  to  provide  fully  for  such  schools  as  are  favored  with  ample 
time  for  laboratory  work.  The  authors  believe  that  these  exercises 
will  be  found  to  furnish  a  typical  range  of  experiments  suitable  for 
an  elementary  course.  Though  practical  and  industrial  applications 
receive  considerable  attention,  yet  a  sound  knowledge  of  the  funda- 
mental facts  and  principles  of  the  science  is  considered  of  most  im- 
portance to  the  beginner,  since  it  is  only  through  painstaking  labor 
along  theoretical  lines  that  the  achievements  of  industrial  chemistry 
have  been  obtained. 

It  is  hoped  that  the  Manual  will  prove  an  attractive  introduction 
to  the  experimental  determination  of  chemical  facts,  and  will  lead 
the  pupil  to  an  interest  in  chemical  theory  for  its  own  real  and 
permanent  value. 

The  authors  gratefully  acknowledge  indebtedness  to  that  large 
body  of  chemistry  teachers  whose  kind  reception  of  the  "  First  Prin- 
ciples of  Chemistry"  has  encouraged  them  to  publish  the  present 
laboratory  course. 

NEW  YORK,  September,  1908. 

711394 


PREFACE  TO   REVISED   EDITION 

THE  new  edition  of  this  Laboratory  Manual  is  the  result  of  the 
authors'  nine,  years  of  experience  with  the  first  edition ;  it  also  em- 
bodies the  suggestions  of  many  other  chemistry  teachers  throughout 
the  country. 

Such  a  thorough  testing  has  led  to  the  simplification  of  some  ex- 
periments and  to  the  modification  of  others.  A  special  attempt  has 
been  made  to  have  all  questions  on  fact  and  theory  so  simple  that 
the  answers  may  reasonably  be  expected  from  students  of  average 
ability.  Whenever  additional  information  is  needed  to  throw  light 
upon  the  discussion,  it  has  been  freely  furnished. 

A  number  of  new  experiments  have  been  added  in  order  to  offer 
a  greater  range  of  material,  so  that  selections  can  be  made  to  fit  the 
aims  of  a  particular  course.  These  additions  deal  with  both  the 
practical  and  the  theoretical  sides  of  the  subject. 

The  typography  and  the  arrangement  of  the  questions  have  been 
designed  so  as  to  indicate  each  step  in  the  experiments.  Blank 
spaces  for  answers  to  the  questions  and  room  for  drawings  make  pos- 
sible a  use  of  the  book  as  manual  and  laboratory  notebook  combined. 
This  plan  is  growing  in  favor,  since  it  gives  the  student  more  time 
for  experimentation  and  observation  of  laboratory  phenomena.  For 
the  teacher,  on  the  other  hand,  there  is  the  advantage  that  the  cor- 
recting of  notebooks  may  be  done  with  less  drudgery  and  with 
greater  efficiency. 

A  number  of  new  illustrations  have  been  added  .to  lend  interest 
to  the  work  and  to  suggest  to  the  students  a  suitable  assembling  of 
the  apparatus.  Half-tones  have  been  used  in  preference  to  line 
drawings,  so  that  the  student  will  have  to  depend  upon  himself  in 
putting  into  his  laboratory  notebook  the  line  drawings  of  the 
apparatus. 

NEW  JORK,  June,  1917. 


GENERAL  SUGGESTIONS  TO   TEACHERS 

Selection  of  Experiments.  —  The  time  usually  allotted  to  the  labo- 
ratory work  in  the  first  course  in  Chemistry  is  not  sufficient  for 
performing  all  the  experiments  given  in  this  manual.  As  an  aid  in 
the  selection  of  a  well-balanced  course,  the  experiments  are  divided 
into  the  following  groups  : 

GROUP  A.  1,  2,  3,  4,  5,  6,  7,  8,  9,  10,  11,  16,  18, 19,  20,  22,  23,  24, 
26,  27,  34,  36,  37,  38  or  39,  41,  42,  43,  44,  46,  47,  50,  51,  53,  61,  62, 
63,  66,  67,  68,  71,  78,  79,  80. 

GROUP  B.     12,  14,  15,  17,  21,  25,  28,  33,  48,  49,  55  or  56,  64,  65. 

GROUP  C.  13,  29,  30,  31,  32,  35,  40,  45,  52,  54,  57,  58,  59,  60,  69, 
70,  72,  73,  74,  75,  76,  77,  81,  82,  83,  84. 

It  is  recommended  that  all  students  be  required  to  perform  the  ex- 
periments of  Group  A.  These  experiments  are  fundamental  in  their 
nature,  and  very  valuable  as  a  means  of  laboratory  instruction.  This 
list,  together  with  a  certain  number  of  experiments  from  Group  B, 
will  satisfy  the  usual  college  entrance  requirement  in  Chemistry. 

Most  instructors  will  doubtless  assign  to  their  classes  a  good 
portion  of  the  exercises  in  Group  B.  The  several  quantitative  ex- 
periments in  this  subdivision  are  valuable  for  their  training  in 
manipulation,  for  the  theory  they  illustrate,  and  for  the  interest 
they  arouse. 

It  is  hoped  that  every  laboratory  section  will  find  time  for  some 
of  the  experiments  in  Group  C,  particularly  those  dealing  with  the 
practical  applications  of  Chemistry. 

The  Directions  for  the  Experiments.  —  At  first  the  directions  for  the 
laboratory  operations  are  somewhat  detailed.  This  plan  has  been 
followed  in  order  that  the  beginner  may  have  the  help  needed  to 
perform  the  experiment  readily  and  intelligently.  As  the  student 
gains  in  experience  and  self-reliance,  the  directions  become  less  full. 

vii 


Vlll  GENERAL   SUGGESTIONS   TO   TEACHERS 

All  the  questions  have  been  put  in  italics  so  Jbhat  the  student  will 
realize  their  importance.  They  should  be  answered  in  regular  order 
for  two  reasons  :  (1)  so  that  the  student  will  understand  what  he  is 
doing  at  the  time  the  question  is  asked ;  and  (2)  so  that  he  may 
have  information  needed  for  later  parts  of  the  experiment.  The 
authors  have  taken  great  care  to  avoid  questions  that  the  student 
cannot  fairly  or  legitimately  answer  from  the  experimental  data, 
and  they  have  not  hesitated  to  give  fact  or  theory  when  these  are 
necessary  to  a  fair  comprehension  of  the  questions.  Formulas  for 
products  new  to  the  experience  of  the  student  have  been  given  in 
the  form  of  equations  to  be  completed. 

When  Class  Discussion  appears  in  parentheses,  it  means  that  the 
student  requires  further  information  in  order  to  give  a  complete  an- 
swer. Such  information  is  often  best  furnished  in  a  class  discussion. 

When  a  separate  notebook  is  used,  the  tabular  forms  for  numerical 
data  should  be  written  in  at  the  beginning  of  the  experiment,  so 
that  the  measurements  may  be  recorded  as  soon  as  they  are  made. 
Some  instructors  find  it  advantageous  to  have  the  students  put  in 
the  tabular  forms  before  coming  into  the  laboratory. 

Apparatus  and  Material.  —  It  has  been  the  aim  of  the  authors  to 
use  such  simple  forms  of  apparatus  as  are  commonly  found  in  the 
ordinary  laboratory  equipment.  For  their  general  availability,  at- 
tention is  called  to  the  agate  pans  and  the  Syracuse  form  of  watch 
glasses.  This  watch  glass  is  superior  to  glass  plates  for  covering 
and  handling  bottles  of  gas.  Although  the  brass  capsule,  ramrod, 
and  holder  used  in  Experiments  9  and  17  can  be  purchased,  many 
instructors  will  prefer  to  have  them  made  in  the  laboratory  shop. 
Accordingly,  directions  for  making  them  are  inserted  here. 

The  sodium  capsule  is  made  either  (a)  by  cutting  y  brass  tubing 
(-yV'  wall)  into  pieces  about  an  inch  long,  and  soldering  into  one  end 
a  brass  disk  y  thick ;  or  (6)  by  drilling  -f^"  brass  rod  with  a  -J-"  or 
Ty  drill.  The  latter  can  be  readily  done  by  mounting  the  rod  in  a 
draw-in  chuck  in  a  lathe,  first  drilling  and  then  cutting  off. 

The  handle  consists  of  a  piece  of  No.  14  copper  or  brass  wire.  A 
few  turns  are  wrapped  tightly  around  the  capsule,  and  about  8"  of 
the  wire  project  at  right  angles  to  the  capsule.  The  outer  end  of 


GENERAL   SUGGESTIONS   TO   TEACHERS  ix 

the  wire  should  either  be  bent  into  a  flat  loop  or  be  forced  into  a 
short  piece  of  dowel  rod. 

A  ramrod  of  iron  or  brass,  about  5"  long,  sliding  easily  into  the 
capsule,  should  be  provided. 

In  the  lists  of  material,  concentrated  acid  means  acid  of  the  indi- 
dicated  specific  gravity  :  hydrochloric  acid,  1.19,  sulphuric  acid,  1.84, 
and  nitric  acid,  1.42.  The  concentrated  ammonia  water  should  have 
a  specific  gravity  of  0.90. 

For  dilute  acids  and  ammonium  hydroxide  the  authors  commonly 
employ  the  following  concentrations  :  — 

Ammonium  hydroxide  (1:4),  that  is,  one  part  by  volume  of  con- 
centrated ammonia  water  to  four  volumes  of  water. 

Hydrochloric  acid  (1 : 4) 

Nitric  acid  (1 :  4) 

Sulphuric  acid        (1 :  6) 

Early  in  the  course,  all  students  should  be  given  definite  directions 
for  the  safe  mixing  of  concentrated  sulphuric  acid  with  water.  The 
required  amount  of  water  should  be  measured  out.  Then  small  por- 
tions of  the  concentrated  acid  should  be  poured  slowly  into  the  water, 
and  the  mixture  should  be  agitated  after  each  addition. 

In  many  cases  special  concentrations  for  acids  and  other  solutions 
are  given  at  the  head  of  the  experiment.  When  no  concentration  is 
expressed,  one  to  ten  is  understood,  that  is,  one  part  by  weight  of 
the  chemical  to  ten  parts  by  weight  of  water.  (A  cubic  centimeter 
of  water  at  ordinary  temperature  is  considered  to  weigh  one  gram.) 
In  the  majority  of  cases,  however,  one  to  twenty  solutions  will  be 
found  to  work  quite  as  well  as  the  one  to  ten,  with  a  consequent 
saving  of  reagents. 

It  will  be  found  convenient  to  have  ready  for  the  students  when 
they  come  into  the  laboratory  the  solutions  listed  in  the  Material  for 
the  various  experiments. 

Several  of  the  experiments  require  solid  chemicals  in  small 
amounts.  In  such  cases,  the  authors  have  often  found  it  advisable 
to  distribute  the  chemicals  on  labeled  slips  of  paper  (about  5  X  10 
cm.),  arranged  in  places  easily  accessible  to  the  students. 

In  taking  specified  quantities  of  solutions,  students  may  need 
graduates  in  some  cases ;  but  more  frequently  the  necessary  quan- 


X  GENERAL   SUGGESTIONS   TO   TEACHEES 

tity  may  be  measured  as  a  fraction  of  a  test-tubeful.     The  ordinary 
test-tube  (6  x  f ")  contains  30  cc. 

In  cases  when  only  one  or  two  cubic  centimeters  of  a  solution  are 
to  be  taken,  the  solutions  can  be  drawn  from  burettes,  which  should 
be  labeled  and  accessible. 


CONTENTS 

PACK 

Care  and  use  of  apparatus .         .  1 

Drawings 3 

Laboratory  work  and  its  record          ......  5 

EXPERIMENT 

1 .  Setting  up  apparatus 7 

2.  Heating  of  metals  in  air 10 

3.  Weight  change  on  heating  a  metal 12 

4.  Decomposition  of  a  compound  formed  by  heating  a  metal  in 

air 14 

5.  Determination  of  the  percentage  of  oxygen  in  air          .         .  16 

6.  Preparation  of  oxygen        .         .         .         ...         .         .19 

7.  Formation  of  oxides 21 

8.  Electrolysis  of  water 23 

9.  Decomposition  of  water  by  sodium 25 

10.  Preparation  of  hydrogen 26 

1 1 .  Properties  of  hydrogen       .         .         .         .         .         .         .28 

12.  Distillation  of  water 30 

13.  Solution  and  suspension 33 

14.  Temperature  and  relative  solubility     .....  35 

15.  Water  of  crystallization 37 

16.  Equivalent  of  magnesium 

17.  Equivalent  of  sodium         .         .         .         . 

18.  Preparation  and  properties  of  chlorine 

19.  Preparation  and  properties  of  hydrochloric  acid   . 

20.  Test  for  a  chloride 51 

2 1 .  Weight  of  a  liter  of  oxygen 54 


xii  CONTENTS 

EXPERIMENT  PAGE 

22.  Bases 57 

23.  Alkalies 61 

24.  Neutralization 64 

25.  Titration 67 

26.  Types  of  chemical  change.     Direct  combination.     Simple 

decomposition   ........  70 

27.  Types  of  chemical  change.     Simple  replacement         .         .  73 

28.  Types  of  chemical  change.     Double  decomposition     .         .  76 

29.  Salts  that  are  not  neutral 79 

30.  Flame   tests 82 

3 1 .  Preparation  of  an  acid  salt          ......  84 

32.  Preparation  of  sodium  carbonate         .....  85 

33.  Determination  of  water  of  crystallization      ....  86 

34.  Forms  of  sulphur 89 

35.  Preparation  of  metallic  sulphides 92 

36.  Preparation  arid  properties  of  hydrogen  sulphide            .         .  94 

37.  Sulphur  dioxide,  sulphite  method        .....  96 

38.  Sulphur  dioxide,  reduction  method 99 

39.  Properties  of  sulphuric  acid 102 

40.  Preparation  of  nitrogen 106 

41.  Preparation  and  properties  of  ammonia       .         .         .         .109 

42.  Ammonium  compounds Ill 

43.  Preparation  and  properties  of  nitric  acid      .         .         .         .115 

44.  Preparation  and  properties  of  nitric  oxide    .         .         .         .118 

45.  Preparation  and  properties  of  nitrous  oxide          .         .  121 

46.  Preparation  and  properties  of  bromine         .         .         .         .123 

47.  Preparation  and  properties  of  iodine 126 

48.  The  halogen  acids 129 

49.  Destructive  distillation 132 

50.  Properties  of  carbon 135 

51.  Preparation  and  properties  of  carbon  dioxide        .         .         .138 


CONTENTS  xiii 

EXPERIMENT  PAQK 

52.  Chemical  fire  extinguisher         .         .  ,         .  •      .     141 

53.  Hard  waters ...     144 

54.  Baking  powders 148 

55.  Preparation  and  properties  of  carbon  monoxide    .         .         .152 

56.  Preparation  and  properties  of  carbon  monoxide,  oxalic  acid 

method 154 

57.  Borax  and  boric  acid 157 

58.  Water  softening        . 160 

59.  Bleaching  of  cotton 163 

60.  Four  ways  of  preparing  a  salt,  sodium  chloride    .         .         .166 

61.  Cobalt  nitrate  tests   . 170 

62.  Borax  bead  tests '172 

63.  Identification  of  simple  salts 174 

64.  Action  of  metals  on  salt  solutions 176 

65.  Equivalent  of  silver  . 179 

66.  Tests  for  iron  salts   .         . 182 

67.  Action  of  a  reducing  agent  on  a  ferric  salt  .         .         .         .184 

68.  Action  of  an  oxidizing  agent  on  a  ferrous  salt       .         .         .186 

69.  Iron  salts  in  photography  —  blueprints         .         .         .         .187 

70.  Silver  salts  in  photography  .         .         .       '  .         .         .190 

71.  Aluminum  hydroxide          .         .         .         .         .         .         .192 

72.  Dyeing:  substantive,  salt,  or  direct  colors  .         .         .         .194 

73.  Dyeing:  acid  colors 198 

74.  Dyeing:  basic  colors .201 

75.  Double  salts 204 

76.  Qualitative  separation  of  lead,  silver,  and  mercury       .         .210 

77.  Chromium  compounds 214 

78.  Fermentation 216 

79.  Preparation  of  ethereal  salts 220 

80.  Soap  making    .........     222 

81.  Starch  223 


xiv  CONTENTS 

KXPEEIMENT  PAGE 

82.  Food  constituents.     Fats.     Proteins .  226 

83.  Food  constituents.     Carbohydrates 228 

84.  Constituents  of  milk 231 

APPENDIX 

Physical  Constants  of  the  Important  Elements    .         .         .  234 

Table  of  Solubilities 236 

General  Rules  for  Solubility 237 

Volatility  of  Compounds 237 

Weight  of  a  Liter  of  Common  Gases          ....  237 

The  Metric  System 238 

Pressure  of  Water  Vapor 240 

List  of  Supplies 241 


LABORATORY   EXERCISES 

IN 

CHEMISTRY 


LABORATORY   EXERCISES   IN    CHEMISTRY 

CARE  AND    USE   OF   APPARATUS 

THE  accompanying  picture  (Figure  1)  gives  the  student 
the  names  of  pieces  of  apparatus  with  which  he  is  not  familiar. 
These  articles  should  be  kept  in  a  clean  and  orderly  condition; 
good  results  cannot  otherwise  be  secured. 


Figure  1 .     Laboratory  apparatus  in  common  use. 

«,  test  tube  rack;  b,  bunsen  burner;  c,  mortar  and  pestle;  d,  watch  glass  (Syracuse) ;   e,  thistle 
tube  ;  /,  flask ;  g,  crucible  ;  h,  reagent  bottles ;  j,  evaporating  dish  ;  k,  funnel ;  I,  beakers. 

The  Burner.  —  The  bunsen  burner  should  burn  with  a  clear, 
blue  flame.  The  ordinary  gas  flame  deposits  soot  on  objects 
which  it  touches.  The  character  -of  the  flame  is  regulated  by 
adjusting  the  quantity  of  air  that  enters  the  holes  at  the  base 
of  the  burner.  The  flame  sometimes  "  strikes  back,"  that  is, 
begins  to  burn  at  the  base  where  the  air  enters.  This  means 

1 


2  LABORATORY  EXERCISES 

that  too  large  a  proportion  of  air  is  entering  the  tube.  Give 
the^rubber  -tubing  a  sudden,  sharp  blow  with  the  edge  of  the 
hand.1  If  successful-,  you  will  extinguish  the  flame  at  the  base 
•of  Jthe^  b\irjier  :'and;  produce  a  colorless  flame  at  the  top  of  the 
'burner.  "  If  not;  successful,  turn  off  the  gas,  adjust  the  movable 
ring,  and  relight  the  burner. 

Heating  Glassware.  —  Test  tubes  may  be  put  directly  in  the 
flame  ;  beakers  and  flasks  should  be  protected  by  wire  gauze 
or  asbestos  mat.  When  glass  apparatus  contains  a  liquid,  the 
flame  should  never  extend  above  the  liquid  in  the  vessel.  Never 
attempt  to  heat  articles  made  of  thick  glass,  such  as  bottles  and 
battery  jars,  because  the  poor  conductivity  of  glass  causes  un- 
equal expansion  and  breakage. 

Heating  Porcelain.  —  Evaporating  dishes  and  crucibles  can  be 
heated  to  very  high  temperatures.  Crucibles  can  be  put  di- 
rectly in  the  flame,  but  evaporating  dishes  should  be  placed  on 
wire  gauze  with  asbestos  center.  In  both  cases  the  heat  should 
be  applied  slowly  at  first. 

Setting  up  Apparatus.  —  (#)  Have  everything  firmly  arranged 
and  securely  placed. 

(5)  Place  the  weight  of  the  object  directly  over  the  base  of 
the  ring-stand. 

(<?)  Have  the  rod  of  the  ring-stand  away  from  you,  not  to- 
ward you. 

(cT)  All  glass  apparatus  should  be  loosely  clamped. 

(e)  See  that  rubber  stoppers  fit  securely,  but  use  care  in 
pressing  them  into  the  necks  of  thin  glass  articles. 

(/)  Never  try  to  push  a  glass  tube  through  the  hole  in  a 
stopper.  Moisten  the  end  of  the  tube,  and  work  it  slowly 
through  the  hole,  with  constant  turning. 

(ff)  The  lower  end  of  a  thistle  tube  should  dip  under  the 
surface  of  the  liquid  in  the  bottle  or  flask. 

(Ji)  The  bends  in  glass  tubes  should  be  rounding,  not 
angular.  The  latter  are  likely  to  break  and  the  flow  of  a  gas 
in  them  is  partly  obstructed. 


DRA  WINGS 


3 


(/)  Pay  a  good  deal  of  attention  to  the  '  appearance '  of  your 
apparatus.  Have  vertical  lines  vertical;  horizontal  lines 
horizontal. 

(/)  Keep  pieces  of  clean  muslin  in  your  locker.  The  direc- 
tions frequently  call  for  dry  tubes  and  bottles. 

(6)  Do  not  lay   a   stopper   from  a  reagent  bottle   on   the 
laboratory  table.     Remove  the  stopper  from  the  bottle  by  press- 
ing the  top  of  the  stopper  between  the  lower  joints  of  the 
second  and  third  fingers  having  the  palm  of  the  hand  upward. 
This  leaves  the  thumb  and  forefinger  for  grasping  the  bottle. 

(7)  After  pouring  from  a  reagent  bottle  remove  the  drop  of 
liquid  usually  sticking  to  its  lip  by  touching  it  to  the  top  of 
the  receiving  vessel. 

Detailed  directions  for  cutting,  bending,  and  "fire-polish- 
ing "  glass  tubing  are  given  in  Experiment  1. 


DRAWINGS 


The  purpose  of  drawings  in  the  laboratory  note  book  is  not 
to  make  a  picture  of  the  apparatus,  but  to  show  that  the  pupil 
understands  how  it  works.  For  this  reason,  and  also  for  the 


Figure  2. 

sake  of  simplicity,  make  sectional,  not  perspective  drawings. 
To  illustrate  this,  a  test  tube  and  a  bottle  are  shown  drawn  in 


LABORATORY  EXERCISES 


both  ways   (Figure  2).     It  will  be  readily  seen  that  in   each 
case  the  sectional  is  the  simpler  of  the  two  drawings. 

In  making   a   sectional   drawing,  imagine   a   vertical   plane 

passing  through  the  middle  of  your 
apparatus ;  then  imagine  your 
paper  to  be  in  the  position  of 
this  plane.  Trace  lines  where  the 
paper  would  touch  the  inter- 
sected apparatus.  The  accom- 
panying diagram  (Figure  3)  is  a 
sectional  drawing  of  the  appa- 
ratus used  in  the  preparation  of 
Figure  3.  hydrogen. 

Notice  carefully  the  following  points  : 

(a)  The  bottom  of  the  pan,  in  which  the  gas-collecting  bottle 
stands,  is  represented  by  a  horizontal  straight  line ;  in  a  per- 
spective drawing  this  would  be  a  curved  line.  The  bottoms  of 
bottles,  flasks,  etc.,  are  always  represented  by  straight  lines. 

(£)  The  rubber  stopper  is  indicated  by  cross  hatching 
(parallel  oblique  lines). 

(c)  Water  or  other  liquid  is  represented  by  short  horizontal 
lines. 

(c?)  A  line  is  not  drawn  for  the  top  edge  of  the  thistle  tube, 
since  this  would  not  show  in  the  imaginary  section.  A  like 
thing  is  true  for  all  open  bottles  and  flasks.  Thus  it  is  possible 
to  show  a  passageway  for  the  gases  through  the  apparatus. 

The  pupil  should  aim  for  skill  in  making  these  sectional 
drawings  rapidly  without  the  use  of  a  stencil. 


LABORATORY   WORK  5 

LABORATORY   WORK  AND   ITS   RECORD 

Object.  —  The  purpose  of  a  laboratory  is  to  bring  the  student 
in  contact  with  the  material  studied.  This  gives  a  real  knowl- 
edge of  chemical  action  that  book  study  alone  cannot  furnish. 

See,  therefore,  all  that  goes  on  before  you.  Then,  think 
about  what  you  see. 

Italicized  questions  in  the  laboratory  directions  direct  your 
attention,  sometimes  to  what  you  should  see,  sometimes  to  the 
meaning  of  things  seen. 

Note  Book  Record.  — The  record  of  the  laboratory  work  con- 
sists of  the  making  of  drawings,  the  answering  of  the  italicized 
questions,  and  the  filling  in  of  tabular  forms. 

In  case  you  use  this  book  for  your  laboratory  record,  care- 
fully write  all  that  is  called  for,  using  single  words  or  phrases 
when  these  will  answer  the  questions.  When  a  longer  record 
is  required,  form  a  clear,  well-arranged  sentence  in  your  mind 
before  setting  it  down. 

In  case  a  separate  note  book  is  used  for  the  laboratory  record, 
state  in  your  own  words  what  you  have  done  and  what  you  have 
seen.  Avoid  copying  the  laboratory  directions,  but  write 
simple  sentences  stating  what  has  been  done  and  its  result. 
This  will  give  a  short,  clear  record. 


EXPERIMENT  1 
Setting  up  Apparatus 

APPARATUS.  Ring- stand,  with  ring  and  clamp ;  flask,  250  cc.;  thistle 
tube  ;  2-hole  rubber  stopper  to  fit  flask ;  piece  of  glass  tubing  23" 
long ;  bunsen  burner ;  wing  top  for  burner ;  triangular  file  ;  asbestos 
square;  pan;  rubber  connection,  1"  long;  wire  gauze,  asbestos 
center. 

(a)  Divide  the  piece  of  glass  tubing  into  two  parts,  one 
about  6  inches  long,  the  other  about  17  inches.  '  To  do  this 
make  a  scratch  with  one  forward 
stroke  of  a  triangular  file  on  one 
side  of  the  tubing  at  the  point 
where  you  desire  to  cut  it.  Hold 
the  tube  in  both  hands  with  the 

Figure  4. 

two    thumb    nails    opposite   the 

scratch.  Bend  the  ends  of  the  tubing  toward  you,  at  the  same 
time  pulling  the  hands  apart  (Figure  4).  The  result  should 
be  a  clean  cut  at  right  angles  to  the  length  of  the  tube. 

Place  the  wing  top  on  the  bunsen  burner.     Light  the  burner, 
and  turn  .the  ring  at  the  bottom. 
What  effect  has  this  on  thejlame  ? 


Adjust  the  ring  so  that  the  flame  is  blue.  Hold  the  short 
piece  of  tubing  in  the  flame  so  that  two  inches  of  the  middle 
portion  will  be  heated.  Slowly  rotate  the  tube  between  your 
fingers  so  that  all  sides  are  evenly  heated.  After  the  heated 
part  has  become  quite  soft,  take  the  tube  out  of  the  flame,  and, 
without  too  much  haste,  bend  it  so  that  the  arms  make  a  right 
angle.  See  to  it  that  the  arms  are  in  the  same  plane ;  to  do 
this,  sight  the  tube  sideways.  Lay  the  tube  aside  on  the 
asbestos  square  to  cool.  The  bend  should  be  rounding  and  not 
sharply  angular. 
Why  ? 

<t^l£^  Ats^^d^^ 


8 


LABORATORY  EXERCISES 


After  the  tube  has  become  cool  enough  to  hold  it  at  the  bend, 
fire  polish  it  at  both  ends.     To  do  this  hold  the  end  in  the 

upper  part  of  the  flame,  point- 
ing it  downward  as  much  as 
possible,  until  the  flame  turns 
yellow.  This  is  an  indication 
that  the  glass  has  begun  to 
soften. 

Bend  the  long  piece  of  tub- 
ing in  a  similar  way,  having 
the  bend  about  three  inches 
from  one  end.  Fire  polish 
both  ends. 

(6)  Set  up  the  apparatus 
shown  in  Figure  5,  paying 
attention  to  the  following 
points : 

(1)  Place     the     ring-stand 
with  the  vertical    rod   at   the 
back,  not  the  front. 
•,-T-i-rf  /«- 


Figure  5. 


Why? 


(2)  Have  the  ring  and  what  it  supports  directly  above  the 
,  not  at  one  side. 
Why? 


(3)  The   ring   should   be  placed  at  such  a  height  that  the 
wire  gauze  which  it  supports  will  strike  the  flame  at  the  tip  of 
the  inner  blue  cone. 

(4)  Adjust  the  clamp  so  that  it  holds  the  flask  firmly,  but 
with  a  very  light  pressure.     Glass  used  for  chemical  apparatus 
is  as  fragile  as  other  glass. 

(5)  Moisten  the  end  of  the  thistle  tube  and  work  it  slowly, 


SETTING   UP  APPARATUS  9 

with  constant  turning,  into  one  of   the  holes  of  the   stopper. 
Never  try  to  push  a  thistle  tube  through  a  stopper. 
Why? 


(6)  Adjust  the  thistle  tube  so  that  its  lower  end  is  a  quarter 
of  an  inch  from  the  bottom  of  the  flask. 

(7)  Place  the  short  right  angle  bend  in  the  other  hole  of  the 
stopper,  and  connect  the  long  bend  by  means  of  a  short  piece  of 
rubber  tubing. 

Pour  a  test  tube  of  water  into  the  flask  through  the  thistle 
tube.  Heat  the  water  till  it  boils. 

TJirough  which  tube  does  the  steam  issue  ? 

Why  should  a  thistle  tube  always  dip  into  the  liquid  in  the  flask  9 
V  "/H^J^f 

^jc         f 

Stopper  the  end  of  the  delivery  tube  for  a  moment. 
What  happens  in  the  thistle  tube  9 

Let  the  delivery  tube  dip  under  the  surface  of  water  in  a 
pan.  Again  boil  the  water  in  the  flask.  Then  take  away  the 
bunsen  flame. 

What  happens  at  the  lower  end  of  the  thistle  tube  as  the  steam  in 

the  flask  cools  9 

Wfiat  would  happen  in  this  case  if  the  flask  carried  only  a  delivery 
tube  without  the  thistle  tube  9 


If  you  do  not  know,  repeat  the  operation,  holding  the  palm  of 
the  hand  over  the  upper  end  of  the  thistle  tube  while  the  con- 
tents of  the  flask  are  cooling. 
Result  9 

In  what  two  ways  does  the  thistle  tube  act  as  a  safety  device  9 


10  LABORATORY  EXERCISES 

EXPERIMENT   2 

Heating  of  Metals  in  Air 

APPARATUS.  Bunsen  burner  ;  forceps  ;  ring-stand  with  one  ring ;  pipe- 
stem  triangle  ;  lid  of  porcelain  crucible  ;  iron  wire  15  cm.  long. 

MATERIAL.  Copper  strips  (5  cm.  x  1  cm.  x  0.5  cm.)  or  #24  copper 
wire  ;  magnesium  ribbon,  6  cm.;  granulated  tin;  sandpaper,  #  1. 

O)   Copper. 

Scour  a  piece  of  copper  with  sandpaper.  Examine  the  bright 
copper,  noting  its  color,  luster,  and  flexibility.  Take  hold  of 
one  end  of  the  copper  with  forceps,  and  hold  the  other  end  in 
the  outer  flame  of  the  burner  until  it  is  red  hot.  Remove  the 
strip  from  the  flame  and  watch  it  while  cooling.  Bend  the  strip. 

Compare  the  properties  of  the  surface  material  with  those  observed 
in  the  original  copper  and  record  in  the  table  below. 

(5)  Magnesium. 

Examine  a  piece  of  magnesium  ribbon,  noting  its  color,  luster, 
and  flexibility.     Using  forceps,  take  hold  of  one  end  of  the 
magnesium,  and  place  the  free  end  of  the  ribbon  in  the  flame. 
Result  ? 


Compare  the  product  ivith  the  magnesium  and  record  your  observa- 
tions in  the  table. 

O)   Tin. 

Place  the  lid  of  a  porcelain  crucible  on  a  pipe-stem  triangle, 
supported  on  a  ring-stand.  On  the  crucible  lid  put  a  few 
pieces  of  granulated  tin,  and  heat  gently  at  first,  keeping  the 
flame  in  motion  and  well  below  the  crucible  lid.  When  the  tin 
melts,  stand  the  burner  beneath  the  crucible  lid  and  stir  the  tin 
constantly  with  an  iron  wire. 

Compare  the  product  with  the  original  tin  and  record  your  observa- 
tions in  the  table. 


HEATING  OF  METALS  IN  AIR 
TABLE 


11 


MATERIAL  EXAMINED 

COLOR 

LUSTER 

FLEXIBILITY 

Copper 

Substance  obtained  by 
heating  copper 

Magnesium 

Substance  obtained  by 
burning  magnesium 

Tin 

Substance  obtained  by 
burning  tin 

Have  chemical  or  physical  changes  taken  place  during  the  heating 
of  the  metals  in  air  f 

Explain. 


12 


LAB  OR  A  TOR  F '  EXERCISES 


EXPERIMENT    3 

Weight  Change  on  Heating  a  Metal 
Each  student  should  perform  but  one  experiment,  a  or  b. 

APPARATUS,     (a)  Porcelain  crucible  ;  horn  pan  balance  ;  shot  or  sand  ; 

pipe-stem  triangle  ;  ring-stand  ;  bunsen  burner  ;  iron  wire. 

(b)  Same  as  for  (a),  except  the  iron  wire. 

MATERIAL,     (a)   Granulated   tin ;    (&)  copper   gauze,   or  copper   wire, 
#30. 


(a)  Tin. 

Counterpoise  on  a  horn  pan  balance  a 
porcelain  crucible  that  contains  about  two 
grams  of  granulated  tin  (Figure  6).  Re- 
move the  crucible,  leaving  the  counter- 
poise on  the  balance. 

Place  the  crucible  on  a  pipe-stem  tri- 
angle. Heat  gently  at  first,  keeping  the 
flame  in  motion  and  well  below  the  cru- 
cible. Gradually  increase  the  heat,  and 
allow  the  crucible  to  remain  so  that  it  is 
just  above  the  tip  of  the  inner  cone  of  the 

flame  for  twenty  minutes.     Stir  in  the  tin  frequently  with  an 
iron  wire. 

Record  any  change  in  appearance. 

Remove  the  burner  and   allow  the   crucible  to  cool  on  the 
triangle. 

Place  the  crucible  on  the  balance. 
Has  there  been  a  loss  or  a  gain  in  weight  ? 

What  explanation  can  be  made  of  the  change  in  weight  ? 
(Consider  the  probability  of  the  air  having  something  to  do 
with  the  change.) 


WEIGHT  CHANGE  ON  HEATING  A  METAL  13 

(5)    Copper- 

Counterpoise  a  porcelain  crucible,  containing  about  2  grams 
of  fine  copper  wire,  or  fine-meshed  copper  gauze  rolled  into  a 
loose  ball. 

Place  the  crucible  on  a  pipe-stem  triangle.  Heat  gently  at 
first,  keeping  the  flame  in  motion  and  well  below  the  crucible. 
Gradually  increase  the  heat  and  then  allow  the  crucible  to 
remain  so  that  it  is  just  above  the  tip  of  the  inner  cone  of  the 
flame  for  thirty  minutes. 

Remove  the  burner,  put  the  cover  on  the  crucible,  and  allow 
it  to  cool  on  the  triangle. 

Place  the  crucible  without  its  cover  on  the  balance. 
Has  there  been  a  loss  or  a  gain  in  weight  ? 

What  explanation  can  be  made  of  the  change  in  weight  ? 
(Consider  the  probability  of  the  air  having  something  to  do 
with  the  change.) 


14 


LABORATORY  EXERCISES 


EXPERIMENT   4 
Decomposition  of  a  Compound  formed  by  Heating  a  Metal  in  Air 

APPARATUS.  Ring- stand  and  clamp ;  hard  glass  test  tube ;  rubber 
stopper ;  delivery  tube  ;  dish  of  water ;  test  tube ;  splinter ;  bunsen 
burner 

MATERIAL.     Mercuric  oxide. 

(a)  Put  about  2  grams  of  the  red  powder  in  a  hard  glass 
test  tube  fitted  with  a  stopper  carrying  a  delivery  tube.     Place 


Figure  7. 

the  end  of  the  delivery  tube  under  the  mouth  of  a  test  tube 
filled  with  water  and  inverted  in  a  dish  of  water  (Figure  7). 
(7»)  Heat  gradually  the  hard  glass  tube. 

What  is  the  cause  of  the  bubbling  when  the  tube  is  first  warmed  V 


Do  not  allow  the  hard  glass  test  tube  to  cool  while  the  mouth  of  the  delivery  tube 
is  under  water. 

Why? 

As  soon  as  one  half  the  water  in  the  inverted  tube  is  dis- 
placed, remove  the  test  tube,  invert  it,  and  insert  a  glowing 
splinter. 


DECOMPOSITION   OF  A   COMPOUND  15 


Result 


(e)  Collect  a  second  test  tube  of  gas  and  test  as  before. 

What  is  the  difference  between  the  behavior  of  the  glowing  splinter 
in  the  two  test  tubes  f 


What  ivas  the  gas  in  the  first  test  tube  9 

The  gas  in  the  second  test  tube  was  oxygen, 
(d)  Take  a  splinter  and  scrape  together  the  substance  which 
has  collected  on  the  cooler  portion  of  the  hard  glass  tube. 

v_^ 

What  is  the  substance  ? 

. 

Of  what  is  the  red  powder  composed  ?  ' 

Complete  the  equation  : 

mercuric  oxide  — »~  '  +  _^_  

. 

SECTIONAL   DRAWING  OF   APPARATUS 


16 


LABORATORY  EXERCISES 


EXPERIMENT   5 

Determination  of  the  Percentage  of  Oxygen  in  Air  (Volumetric) 

APPARATUS.  Glass  cylinder,  about  12"  x  2"  (hydrometer  jar);*  50  cc 
gas-measuring  tube;  #18  copper  wire,  23  cm.  long;  evaporating 
dish  ;  thermometer  ;  barometer. 

MATERIAL.     Yellow  phosphorus. 

Caution !    Yellow  phosphorus  should  never  be  handled  except  under  water. 

(a)  Nearly  fill  a  glass  cylinder  with  water.  Pour  into  a  50 
cc.  gas-measuring  tube  enough  water  so  that  the  water  level 
is  at  a  graduation  mark  near  the  bottom  of  the  tube  when  it  is 
inverted  and  its  mouth  placed  under  the  water  in  the  cylinder. 
In  taking  readings  the  tube  should  be  held  between  thumb  and 
finger  so  as  not  to  heat  the  inclosed  gas,  and  it  should  be  so  ad- 
justed that  the  water  is  at  the  same  level  outside  and  inside. 
Have  your  eye  at  the  level  of  the  water. 

In  a  table  like  that  indicated  below,  record 
the  volume  of  the  inclosed  air  and  its  tempera- 
ture. Get  this  by  taking  the  temperature  of 
the  water,  which  should  have  stood  long 
enough  to  be  at  the  temperature  of  the  room. 
Also  obtain  and  record  the  barometer  reading. 
Applying  Charles*  law  and  Boyle  s  law,  find 
the  volume  that  this  air  would  occupy  at  standard 
conditions  (0°  (7.  and  760  mm.). 

A  Take  to  the  instructor  an  evaporating  dish 

of  water  and  obtain  a  wire  with  a  piece  of 
phosphorus  on  one  end.  Keep  the  phosphorus 
under  water  until  you  reach  your  desk  and  immediately  put 
the  wire  with  the  phosphorus  into  the  cylinder  of  water, 

letting  it  rest  against  the  side  of  the  cylinder 
(Figure  8).  Now  lower  the  gas-measuring 


Figure  8. 


tube  containing  the  measured  volume  of  air  over  the  phos- 
phorus so  that  the  phosphorus  will  be  above  the  middle  of  the 
space  occupied  by  the  air. 


PERCENTAGE  OF  OXYGEN  IN  AIR  17 

Note  and  record  the  action  of  the  phosphorus. 
Is  there  any  change  in  the  level  of  the  water  inside  the  tube  ? 

The  substance  formed  is  phosphorus  oxide,  which  dissolves  in 
the  water. 

Complete  the  equation : 

-h  _ — >-  phosphorus  oxide 

Allow  the  action  to  continue  overnight. 

(5)  The  next  day,  remove  the  tube  from  over  the  phos- 
phorus, but  still  keep  the  mouth  of  the  tube  beneath  the  water. 
Then  raise  or  lower  the  tube  until  the  water  is  at  £he  same 
level  inside  and  outside. 

Read  and  record  in  the  table  the  volume  of  the  gas  remaining  in 
the  tube.  Record  the  temperature  of  the  water  and  the  barometric 
pressure. 

Applying  Charles'  law  and  Boyle  %  law,  find  the  volume  which 
the  gas  that  remains  would  occupy  if  it  ivere  at  standard  conditions. 
The  difference  between  the  original  volume  of  air  inclosed  and 
the  volume  of  gas  that  remains,  both  corrected  to  standard 
conditions,  represents  the  amount  of  oxygen  removed  by  the 
phosphorus.  Calculate  the  -  percentage  of  oxygen  in  the  air. 
Make  all  calculations  in  your  note  book. 

TABLE 


Volume  of  air  taken cc. 

Temperature  of  air  taken °C. 

Pressure  of  air  barometer  reading mm. 

Corrected  volume  of  air cc. 

Volume  of  gas  remaining  in  measuring  tube cc. 

Temperature  of  gas  remaining °  C. 

Pressure  of  gas  remaining  (barometer  reading) mm. 

Corrected  volume  of  gas  remaining cc. 

Volume  of  oxygen  removed  by  phosphorus cc. 

Percentage  by  volume  of  oxygen  in  air % 


LABORATORY  EXERCISES 
CALCULATIONS 


PREPARATION  OF  OXYGEN 


19 


EXPERIMENT   6 
Preparation  01  Oxygen  by  the  Decomposition  of  a  Chlorate 

APPARATUS.  Two  test  tubes ;  delivery  tube ;  rubber  stopper ;  ring- 
stand  with  clamp ;  bunsen  burner ;  four  6-oz.  wide-mouth  bottles ; 
four  glass  plates  for  wide-mouth  bottles  ;  enameled  pan,  or  pneumatic 
trough  ;  watch  glass  ;  funnel. 

MATERIAL.  Potassium  or  sodium  chlorate ;  manganese  dioxide  ;  filter 
paper ;  splinter. 

In  this  experiment  there  is  danger  of  the  water  "  sucking  back  "  into  the  hot  test 
tube.  Guard  against  this  by  removing  the  delivery  tube  from  the  water  before  the 
flow  of  gas  stops. 

(a)  Mix  thoroughly  about  8  grams  of  potassium  chlorate 
and  6  grams  of  manganese  dioxide.  Place  in  a  test  tube  pro- 
vided with  a  delivery  tube.  Clamp  the  test  tube  in  a  position 


-  Figure  9. 

convenient  for  heating  (Figure  9).  If  a  pneumatic  trough  is 
used,  adjust  the  delivery  tube  to  deliver  the  gas  just  below  the 
opening  in  the  bridge  of  the  trough.  Carefully  regulate  the 
heating  so  as  to  cause  a  very  gentle  evolution  of  the  gas.  Do  not 

heat  the  test  tube  sufficiently  to  make  the  flame  yellow. 


20  LABOEATOEY  EXERCISES 

(5)  Collect  a  test-tubeful  of  the  gas  and  test  it  with  a  glow- 
ing  splinter. 
Eesult  ? 


Collect  the  remainder  of  the  gas  in  wide-mouth  bottles. 
Cover  with  glass  tubes  and  keep  for  Experiment  7. 

(c)  Remove  the  delivery  tube  and  allow  the  test  tube  to 
cool.  Nearly  fill  the  test  tube  with  hot  water,  close  the  mouth 
of  the  tube  with  the  thumb,  and  shake  the  tube. 

Pour  the  muddy  liquid  on  a  moistened  filter  paper  fitted  to  a 
funnel.  Collect  the  clear  liquid  (filtrate)  in  a  test  tube. 

Remove  a  small  portion  of  the  black  residue  from  the  filter, 
place  it  on  a  second  watch  glass,  and  set  it  aside  to  dry. 

Which  of  the  original  substances  does  the  black  residue  resemble  f 


Taste  a  crystal  of  potassium  chlorate.     Then  taste  the  clear 
filtrate. 

Do  they  taste  alike  ? 

•fa 

i 
Is  the  substance  in  the  filtrate  potassium  chlorate  or  a  different 

substance  $ 


From  which  of  the  original  substances  was  the  oxygen  probably 
derived  f 

/J  n  Ci-<£4  (  :  wo- 

Complete  the  equation  : 
potassium  chlorate  —  >-  potassium  chloride  + 


[  potassium 


\  chlorine 

1  oxygen  chlonne 


potassium 


The  manganese  dioxide  causes  the  oxygen  to  be  liberated 
more  regularly  and  at  a  lower  temperature. 


FORMATION  OF  OXIDES  21 


t^+t*-  ^#6*4.  -^    s**t<£<9,    , 

EXPERIMENT  7 

Formation  of  Oxides  / 

APPARATUS.     Deflagrating  spoon  ;  asbestos  paper  ;  bunsen  burner. 
MATERIAL.      Four  bottles  of  oxygen  ;  splinter  of  charcoal  ;  magnesium 
ribbon,  5  cm.  long  ;  sulphur  ;  red  phosphorus. 

(«)   Place  a  thin  splinter  of  charcoal  across  the  bowl  of  a 
clean  deflagrating  spoon.     Heat  the  end  of  the  splinter  until  it 
glows  brightly,  and  immediately  lower  it  into  a  bottle  of  oxygen* 
•     Does  the  charcoal  burn  with  aflame  ? 

Compare  the  intensity  of  the  action  in  oxygen  with  that  in  air. 


Of  what  elements  does  the  gas  formed  probably  consist  ? 


(6)  Twine  a  piece  of  magnesium  ribbon  around  the  rod  of 
the  deflagrating  spoon,  allowing  the  upper  end  to  project 
slightl}r.  Light  the  free  end  and  lower  the  spoon  into  a  bottle 
of  oxygen. 

Compare  the  combustion  of  the  magnesium  with  that  of  the  carbon. 

' 
Compare  the  action  in  oxygen  with  that  in  air. 

What  is  the  appearance  of  the  oxide  of  magnesium  ? 

Does  this  seem  to    be  the   same   material  as  that  obtained  when 
magnesium  was  burned  in  air  (Experiment  2)  ? 

(c)  Clean  the  spoon,  line  it  with  asbestos  paper  (baking  sheet), 
and  put  on  the  paper  a  small  piece  of  sulphur.     Heat  the  sulphur 
by  directing  the  flame  of  the  burner  against  it  until  it  lights, 
and  then  lower  it  into  the  bottle  of  oxygen. 
Describe  the  burning  of  the  sulphur  in  oxygen. 

0  *-<? 


22  LABORATORY  EXERCISES 

When  the   mist  (principally  unburned   sulphur)  has  disap- 
peared, very  cautiously  smell  the  contents  of  the  bottle. 
Name  this  gas. 


(d)  Reline  the  spoon,  and  place  on  the  asbestos  a  pinch  of 
red  phosphorus.  Heat  the  phosphorus  until  it  lights,  and  put 
it  into  a  bottle  of  oxygen. 

Describe  the  burning  of  phosphorus  in  oxygen. 


Is  the  2)roduct  a  gas  or  does  it  consist  of  fine  solid  particles  ? 
Name  the  product. 

Make  a  general  statement  as  to  the  relative  rapidity  of  the  burn- 
ing of  a  substance  in  oxygen  and  its  burning  in  air. 


Vf  /  /  ,  • 

Give  a  general  name  for  the  product  formed  by  burning  an  element 
in  oxygen. 

//  ^  ^  f 

(J/  -   i-'U^t- 

Complete  the  equations: 

carbon  +  oxygen          — >- 


magnesium  -f-  oxygen  — >-    /  /,  ,« 
sulphur  4-  oxygen         — >- 
phosphorus  +  oxygen  — >- 


ELECTROLYSIS   OF   WATER 


23 


EXPERIMENT   8 

Electrolysis  of  Water 

APPARATUS.  Electrolysis  apparatus  like  that  shown  in  Figure  10; 
battery  jar,  4  x  5" ;  3  dry  cells  and  connections,  or  100-watt  lamp 
and  socket  with  connections  for  110  volt  direct  current;  bunsen 
burner ;  two  test  tubes. 

MATERIAL.     Sulphuric  acid,  1  to  20 ;  splinter. 

(0)  In  a  small  battery  jar,  place  water 
containing  1  part  of  sulphuric  acid  to  20  of 
water.  The  use  of  the  acid  is  to  make  pos- 
sible the  passage  of  the  current  through  the 
water. 

Set  the  electrolysis  block  firmly  on  one 
side  of  the  jar  (Figure  10).  Fill  two 
test  tubes  with  a  mixture  of  acid  and  water, 
cover  the  end  of  each  tube  in  turn  with 
your  forefinger,  and  invert  it  into  the  water 
of  the  battery  jar.  Remove  the  finger  after 
the  mouth  of  the  test  tube  is  below  the 
surface  of  the  water.  Slip  each  tube  into 
the  clamp  on  one  side  of  the  small  board  and  carefully  push  it 
down  over  the  electrode  until  the  latter  is  entirely  within  the 
tube.  Thoroughly  rinse  the  hands  to  remove 
all  traces  of  acid. 

(6)  Connect  the  two  binding  posts  with  a 
battery  of  three  dry  cells  in  series,  or  with 
a  110-volt  direct  current  circuit,  having  a 
100-watt  incandescent  lamp  in  series  between 
the  source  of  current  and  the  electrolysis 
apparatus  (Figure  11).  Determine  the  di- 
rection of  the  current  as  directed  by  the  instructor.  The 
electrode  through  which  the  current  enters  is  the  anode  (  +  )• 
The  current  leaves  the  solution  at  the  cathode  (  —  ). 


Figure 


I  1 

I 

p. 

f~Y 

In 

I 

y 

Figure  11. 

24  LABORATORY  EXERCISES 

As  soon  as  the  water  in  one  of  the  tubes  has  been  displaced 
by  gas,  remove  the  tube  from  the  battery  jar,  keeping  it  mouth 
downward.     Hold  the  mouth  of  the  tube  to  a  flame. 
Result?     d  M, 


.      .'  •-— 

When  the  other  tube  has  filled  with  gas,   close  it  with  the 
thumb  and  remove  it  from  the  battery  jar,  inverting  it  at  the 
same  time.     Insert  a  glowing  splinter  into  the  gas. 
Result  ? 


What  gas  collects  at  the  anode  ? 

Is  the  same  gas  liberated  at  the  cathode  ? 

(<?)  Refill  the  tubes  with  acidulated  watef  and   again  place 
them  over  the  electrodes. 

How  does  the  amount  of  gas  liberated  at  the  anode  compare  with 
the  amount  liberated  at  the  cathode  1  - 


There  is  the  same  amount  of  sulphuric  acid  at  the  end  of  the 
experiment  as  at  the  beginning. 
Where  did  the  gases  come  from  ? 


Complete  the  equation  : 
water  —  >- 


DECOMPOSITION  OF   WATER  BY  SODIUM 


25 


EXPERIMENT   9 
Decomposition  of  Water  by  Sodium 

APPARATUS.     Brass  capsule,  provided  with  a  holder  ;  brass  ramrod  to 

fit  capsule  ;  pan  ;  test  tube  or  bottle  ;  bunsen  burner. 
MATERIAL.     Sodium. 

Caution  !    The  action  of  sodium  with  water  is  very  violent.    Avoid  danger  by  fol- 
lowing directions. 

Nearly  fill  a  metallic  capsule  with  freshly  cut  sodium  from 
which  all  the  crust  has  been  removed.     The  sodium  must  be  pressed 

firmly  into  the  capsule. 

Place  the  capsule  in  a  wire 
holder,  and,  holding  the  cap- 
sule mouth  downward,  thrust 
it  under  the  mouth  of  an  in- 
verted test  tube  or  small  wide- 
mouth  bottle  filled  with  water. 
Control  the  evolution  of  the 
Fisure  12-  gas  by  slightly  inclining  the 

capsule  (Figure  12).     If  careless  handling  allows  the  sodium 
to  escape  from  the  capsule,  stand  aside. 

When  the  test  tube  is  filled  with  gas,  carry  it  mouth  down- 
ward to  a  flame. 

Remit  f 

4    v  /     / 

of  <wy  c4s*tf~)^*^  ' 

This  gas  is  hydrogen.     The  yellow  color  of  the  flame  is  due 
to  sodium.     Sodium  is  an  element.  j_ 

Where,  does  the  hydrogen  come  from  f  ^l^^f^- 


Complete  the  equation:    , 

**          T  /*- 

sodium  4-  water  — *-   /  -  '/\/.*  /  y  : 

( hydrogen 


-fsodium  hydroxide 


\ oxygen 


f  sodium 
j  hydrogen 
( oxygen 


26 


LABORATORY  EXERCISES 


EXPERIMENT   10 
Preparation  of  Hydrogen  by  the  Reaction  between  an  Acid  and  a  Metal 

APPARATUS.     Wide-mouth  bottle,  8  oz.;  two-hole  stopper  ;  thistle  tube  ; 

delivery  tube  ;  pneumatic  trough  ;  three  wide-mouth  bottles,  6  oz.; 

three  glass  plates  ;  watch  glass  ;  beaker,  250  cc.  ;  test  tubes  ;  ring- 

stand  with  large  ring  ;  bunsen  burner. 
MATERIAL.     Zinc  ;  dilute  sulphuric  acid,  1  to  6  ;  copper  sulphate  solu- 

tion. 

Caution  !  A  mixture  of  hydrogen  and  oxygen  (or  air)  is  dangerously  explosive. 
Have  no  light  or  burner  near  your  generator.  Collect  the  gas  in  test  tubes  until  you 
find  that  the  gas  burns  quietly  when  a  flame  is  applied  to  it. 

(a)  Use    a   wide-mouth    bottle    provided    with    a    two-hole 
stopper  carrying  a  thistle  tube  .and  a  delivery  tube  (Figure  13). 
Wliy  must  the  end  of  the  thistle  tube  dip  below  the  surface  of  the 
liquid  f 

/ 


Have  three  bottles  filled  with 
water,  standing  inverted  in  the 
pneumatic  trough.  Put  about 
20  grams  of  granulated  zinc  into 
the  generator,  and  pour  through 
the  thistle  tube  dilute  sulphuric 
acid  (1  to  6),  until  one  fourth  of 
the  bottle  is  filled. 
Result?  ^t 


./ 

( 


Figure  13. 


If  the  action  is  slow  in  starting,  add  a  few  drops  of  copper 
sulphate  solution  through  the  thistle  tube. 

Observe  and  describe  the  action  in  the  generator. 

7  //>--  Q-'/..  i    ;v  *—  ' 


Under  no  circumstances  add  more  acid,  nor  in  any  way  interfere  with  the  generator 
without  consulting  the  instructor. 


PREPARATION  OF  HYDROGEN  27 

(5)  Collect  the  gas  in  a  test  tube.  As  soon  as  the  test  tube 
is  filled,  hold  it  mouth  downward  to  a  small  flame.  Continue 
to  collect  and  test  the  gas  in  this  manner  until  a  portion  burns 
quietly.  The  hydrogen  is  now  ready  to  be  collected  for  Ex- 
periment 11. 

Fill  three  bottles  with  the  gas.  Leave  them  standing  on  the 
shelf  of  the  pneumatic  trough,  or  cover  them  with  glass  plates 
and  set  them  mouth  downward  on  the  desk. 

H^  Proceed  to  Experiment  11,  part  (a). 

(c)  Filter  a  few  drops  of  the  liquid  in  the  generating  bottle 
into  a  watch  glass.  Place  this  on  the  top  of  a  beaker  one  third 
full  of  water,  and  boil  the  water  until  a  solid  has  appeared  in 
the  watch  glass. 

Examine  this  solid  and  describe  its  appearance. 

The  compound  is  zinc  sulphate,  which  is  composed  of  zinc, 
sulphur,  and  oxygen. 

Complete  the  equation  : 

zinc  +  sulphuric  acid  —  >-  -\- 

f  hydrogen 

|  sulphur 

[oxygen  I  ^   ^ 

From  what  material  does  the  hydrogen  come  ? 
Why  is  the  action  called  a  replacement  action  ?      /. 


Why  icas  the  gas  collected  in  test  tubes  only  and  repeatedly  tested 
in  the  first  part  of  the  experiment  ? 


28 


/£  .^:;£&    -f  //,  .£' 

LABORATORY  EXERCISES 


EXPERIMENT   11 
Properties  of  Hydrogen 

APPARATUS.     Glass  tube  (20  cm.)  ;  test  tube  ;  clamp  ;  bunsen  burner. 
MATERIAL.     Copper  oxide  (wire  form) ;  taper. 

(a)  Replace  the  end  of  the  delivery  tube  of  the  generator  used 
in  Experiment  10  with  a  straight,  dry  glass  tube,  and  let  it  lead 
to  the  bottom  of  a  nearly  horizontal  test  tube  that  contains 
a  little   copper   oxide    (wire 
form)   (Figure  14).      Allow 
the  hydrogen  to  pass  into  the 
tube  for  two  minutes  to  expel 
the  air.     Then  heat  the  tube 
directly    under    the    copper 
oxide. 

When  the  hydrogen  passes 
over  the  heated  copper  oxide, 
what  collects  in  the  cool  portion 
of  the  tube? 


What  is  left  in  the  heated  portion  ? 


Figure  14. 


Hoy)  do  you  account  for  the  production  of  these  substances  ? 


,ff    .<  &<lf'i    "&''((      ' '  >       W/yU  vj  • 

'  element  was  removed  from  the  copper  oxide  by  the  hydrogen  ? 

• 

A  material  which  acts  in  this  way  is  called  a  reducing  agent. 

Complete  the  equation : 
copper  oxide  +  hydrogen  — >-  .  /^  + 

f  copper 
[ oxygen 

(6)  Holding  a  bottle  of  hydrogen  mouth  downward,  thrust 
into  it  a  lighted  taper. 

What  happens  to  the  flame  of  the  taper  ? 


PROPERTIES  OF  HYDROGEN 
What  is  occurring  at  the  mouth  of  the  bottle  9 


29 


Slowly  withdraw  the  taper  from  the  bottle. 

Explain  the  result. 

/    /  J  "  $  / 

'&fr/UAr  x4£-£^£^<     '     '*4,4of~it<w 

^r 

(<?)  Lift  a  bottle  of  hydrogen  and  hold  it,  uncovered  and 
mouth  downward,  for  a  full  minute  by  the  watch.     Then  hold 
the  mouth  of  the  bottle  to  a  flame. 
Result?     iLj 

Hold  another  bottle,  uncovered  and  mouth  upward,  for  a  full 
minute,  and  again  hold  the  mouth  to  the  flame. 
Result  9 

Is  hydrogen  heavier  or  lighter  than  air  9     Give  reasons  for  your 
answer.  ^tu^t- 

Now  return  to  Experiment  10,  part  (<?). 
DRAWING,   PART   (a) 


30 


LABORATORY  EXERCISES 


EXPERIMENT   12 


Distillation  of  Water 

APPARATUS.  Distilling  flask,  250  cc.,  condenser,  and  tubes  as  shown 
in  Figure  15;  r  ing- stand ;  tripod;  one  ring;  clamp;  wire  gauze; 
bunsen  burner  ;  additional  flask  for  distillation  ;  two  beakers,  150  cc., 
or  Erlenmeyer  flasks  ;  two  small  beakers  or  bottles  ;  watch  glass. 

MATERIAL.  Copper  sulphate  crystals;  solution  of  phenolphthalein ; 
ammonia  water  (concentrated). 

Arrange  the  apparatus  as  shown  in  Figure  15.     Connect  one 
of  the  rubber  tubes  to  the  water  faucet  so  that  water  will  enter 


Figure  15. 

the  lower  end  of  the  condenser  ;  let  the  other  drain  into  the 
sink. 

(a)  Put  into  the  distilling  flask  a  few  crystals  of  copper  sul- 
phate and  add  100  cc.  of  water.  Heat  the  contents  of  the  flask 
to  boiling. 

Does  the  copper  sulphate  dissolve  ? 


DISTILLATION  OF    WATER  31 

Give  a  reason  for  your  answer. 


Let  the  distillate  (the  condensed  steam)  collect  in  a  beaker 
or  flask. 

Does  it  contain  any  copper  sulphate  9 
Girt*  a  reason  for  your  answer. 

&&*.,  /' 


Dissolved  solids  in  general  act  in  distillation  as  the  copper 
sulphate  does. 

A  substance  which  readily  changes  into  a  gas  on  being  heated 
is  said  to  be  volatile. 

7s  copper  sulphate  volatile  under  the  conditions  of  this  experiment  ? 

/  J^J     J 

Howdoyojuknow?   , 

^  '  £    x$?U    CU*&tft*+  • 

Can  water  be  purified  from  non-volatile  impurities  by  ilixf  illation? 


(6)   Add  a  drop  of  phenolphthalein  solution  to  some  pure 
water. 

Result  9    T^O     fyrt 


»%&* 


To    100   cc.  of   pure   water   add   one  drop   of  concentrated 
ammonia  water  and  a  drop  of  phenolphthalein  solution. 


Result  ?       '  '&<( 

This  test  is  used  in  this  experiment  to  indicate  the  presence 
of  ammonia  in  water. 

Prepare  another  mixture  of  one  drop  of  concentrated  am- 

monia water  in  200  cc.  of  pure  water.     Pour  it  into  a  clean 

flask  and  distil.      Collect  a  little  of  the  distillate  in  a  clean 

beaker  or  small  bottle.     Add  a  drop  of  phenolphthalein  solution. 

Does  the  distillate  contain  ammonia  9 


LABORATORY  EXERCISES 
Is  ammonia  volatile  f 


Continue  the  distillation  for  two  or  three  minutes  and  then 
collect  a  second  portion  of  the  distillate. 

Does  it  contain  any  ammonia  f 

£L'.'-.t      ;  fJ  ,./,-:*',,- 

Does  the  first  portion  of  the  distillate  contain  more  or  less  ammonia 
than  the  second  portion  ? 

Can  water  be  readily  purified  by  distillation  from  a  volatile  impur- 
ity like  ammonia  ? 

(c?)  Determine,  by  evaporation  on  a  watch  glass  over  steam, 
whether  water  from  the  faucet  contains  non- volatile  impurities. 

Result? 

Suggest  a  method  by  which  salt  water  can  be  converted  into  fresh 
water.  )3 . 

A-'    .  f      ftC"*   **•  ' 

'  DRAWING 


SOLUTION  AND   SUSPENSION  33 

EXPERIMENT   13 
Solution  and  Suspension 

APPARATUS.     Beaker,  250  cc.;   small  battery  jar;  teaspoon  or  horn 

spatula  ;  two  test  tubes  ;  stirring  rod. 
MATERIAL.     Rock  salt ;  fine  salt ;  calcite  ;  powdered  sodium  chromate  ; 

fine  clay  or  precipitated  chalk. 

(a)   Soluble  and  insoluble  substances. 

Put  a  piece  of  rock  salt  about  the  size  of  a  pea  into  a  test 
tube  of  water.  In  another  test  tube  of  water  put  a  lump  of 
calcite  of  equal  size.  Close  the  mouth  of  each  of  the  test  tubes 
and  shake  them. 

Which  substance  disappears  in  the  water  ? 

Which  substance  has  not  dissolved  ? 

How  can  you  tell  this  from  the  shape  of  the  pieces  of  solid  remain- 
ing in  the  water  ?      &&**£  4     ^^H  O^vu 


"  s€&J4  >    ^^•/"1^ 
Name  the  soluble  substance. 

(5)   Distribution  of  the  solute  in  the  solvent. 

Put  half  a  teaspoonful  of  table  salt  in  a  beaker  of  water  and 
stir  the  mixture. 

Is  the  solution  clear  and  transparent  ?      v'"  > 

Dissolve  a  teaspoonful  of  powdered  sodium  chromate  in  a 
beaker  of  water  by  stirring  thoroughly. 
Is  the  solution  clear  f 

Is  it  transparent  f 

What  does  the  uniformity  of  color  indicate  concerning  the  dis- 
tribution of  the   dissolved  substance  (the  solute)  in   the  water  (the 

.'&^</ 


34  LABORATORY  EXERCISES 

• 

Allow  the  solution  to  stand  for  a  short  time. 
Does  the  sodium  chromate  settle  ?      £  if 

Empty    the   beaker  into  the   receptacle   designated   by   the 
instructor. 

((?)   Suspension. 

In  a  battery  jar  of  water  put  a  teaspoonful  of  fine  clay,  or 
precipitated  chalk.     Stir  thoroughly. 
Such  a  mixture  is  called  a  suspension. 
Allow  the  jar  to  stand  for  a  time. 

What  floes  the  solid  in  suspension  tend  to  do  ?  - 


^  / 


What  differences  do  you  note  between  a  suspension  and  a  solution? 

,*/,.*.  &<*../:{  £-v .'  f  *-     ^  -'•'*£  >&•  **A*>>  ^  ' v  j(         y'^-fJ*' 

//  ^  *<?&**  Ws£vT* 

State  three  characteristics  of  a  true  solution  that  have  been  brought 
out  by  this  experiment. 


TEMPERATURE  AND  RELATIVE  SOLUBILITY  35 

EXPERIMENT    14 
Temperature  and  Relative  Solubility 

APPARATUS.     Four  test  tubes  ;  four  small  rubber  bands  ;  bunsen  burner. 
MATERIAL.     Powdered  potassium  nitrate  or  powdered  magnesium  sul- 
phate (Epsom  salts);  fine  salt. 

(a)  Fill  a  test  tube  with  powdered  potassium  nitrate  (salt- 
peter), or  powdered  Epsom  salts.  Add  the  potassium  nitrate, 
a  very  little  at  a  time,  to  another  test  tube  one-fourth  full  of  cold 
water,  shaking  the  test  tube  after  each  addition.  Continue  to 
add  the  potassium  nitrate  until  a  very  little  of  the  solid  re- 
mains after  thorough  shaking. 

Adjust  a  rubber  band  at  the  upper  level  of  the  nitrate  re- 
maining in  the  supply  tube. 

Since  the  cold  water  has  dissolved  all  that  it  can  of  the  potas- 
sium nitrate,  it  is  said  to  be  saturated  with  respect  to  that 
substance  at  the  existing  temperature. 

Heat  in  the  bunsen  flame  the  cold  saturated  solution  of  po- 
tassium nitrate  just  prepared,  and  then  add  more  nitrate  from 
the  supply  tube.  Shake  the  tube  after  each  addition  as  before, 
and  dissolve  in  the  hot  water  as  much  as  you  can  of  the  nitrate. 
During  the  process  keep  the  liquid  hot  by  heating  occasionally 
in  the  flame,  but  take  care  not  to  boil  off  any  of  the  water.  As 
soon  as  the  hot  water  is  saturated  with  nitrate,  set  the  solution 
aside  to  cool  for  later  examination.  Mark,  with  a  second  rub- 
ber band,  the  upper  level  of  the  nitrate  remaining  in  the  supply 
tube. 

How  is  the  amount  of  the  potassium  nitrate  that  can  be  dissolved 

affected  by  increasing  the  temperature  of  the  water  ? 


4u 

M 


ake  a  draining  showing  the  relative  positions  of  the  rubber  bands 
on  the  supply  tube.  Indicate  the  amount  of  the  nitrate  dissolved  re- 
spectively in  equal  volumes  of  cold  and  hot  water. 


.36 


LABORATORY  EXERCISES 


(5)  Examine  the  solution  set  aside  to  cool. 

Describe  what  has  happened. 

/:':  ,\:,         (  #£  f  y.  '<  -^ 

Is  the  amount  of  dissolved  substance  greater  or  less  at  the  lower 
temperature  f 

When  the  liquid  comes  to  the  temperature  of  the  room,  is  it  a  satu- 
rated, or  an  unsaturated  solution  ? 


How  can  you  determine  this  9 


Empty  the  tubes  containing  potassium  nitrate  into  the  recep- 
tacles designed  by  the  instructor. 

(0)  Repeat  part  (a),  using  fine  salt  (sodium  chloride)  in- 
stead of  potassium  nitrate. 

Which  is  increased  the  more  by  increase  in  temperature,  the  solu- 
bility of  sodium  chloride  or  that  of  potassium  nitrate? 


Make  a  statement  concerning  the  relative  solubility  of  salt  in  hot 
and  in  cold  water. 

JU*  &  ' 


DRAWINGS 


•fii 


r 


WATER   OF  CRYSTALLIZATION  37 

EXPERIMENT   15 
Water  of  Crystallization 

APPARATUS.  Horn  pan  balance  ;  two  watch  glasses,  3  in.  ;  counter- 
poise ;  eight  test  tubes  ;  test  tube  rack  ;  bunsen  burner. 

MATERIAL.  Crystallized  sodium  sulphate  ;  copper  sulphate  ;  potas- 
sium chlorate  ;  zinc  sulphate  ;  barium  chloride  ;  potassium  sulphate  ; 
potassium  nitrate  ;  alum. 

(a)  Place  a  small  watch  glass  on  the  pan  of  a  balance  and 
then   add   enough  crystallized    sodium    sulphate    to    counter- 
poise the  weight  placed  by  the  instructor  in  the  other  pan. 
Set  the  crystallized  sodium  sulphate  aside  for  a  half  hour. 
TJien  note  and  record  any  changes  in  its  appearance,    fa, 

^t^a^^^^^^^  ^  ^i^^^u^M 

Again  place  the  watch  glass  and  its  contents  on  the  balance. 
What  does  the  change  in  weight  indicate  ? 

Js-z*  i£  A*>-a    - 

(£>)  Heat  a  few  crystals  of  sodium  sulphate  carefully  in  a 
dry  test  tube,  holding  the  tube  in  a  horizontal  position. 
What  collects  on  the  walls  of  the  test  tube  f 

yasfcu- 

To  what  is  the  change  in  weight  noticed  in  part  (a)  probably  due? 

, 

(<?)  In  another  test  tube,  gently  heat  a  crystal  of  blue  vitriol 
(copper  sulphate)  over  a  small  flame  until  a  white  substance  is 
produced. 

What  important  effects  have  been  produced  as  to  color,  form,  and 

composition  ?    /?. 

-* 


After  cooling,  dissolve  the  residue  in  the  bottom  of  the  tube 
in  a  few  drops  of  hot  water.     Pour  the  solution  on  a  watch 


38 


LABORATORY  EXERCISES 


glass  and  allow  it  to  stand.     Compare  the  final  product  with 
the  original  substance. 
Result?    . 


What  took  place  when  the  copper  sulphate  was  heated  ? 

.  //fe         /tV~cdj/i'      *    >'     ^^j-^CL^.^^^-1^ 

What  happened  when  the  residue  ivas  dissolved   and  allowed  to 
cool?    $J, 

•  •     / 

(d)  In  separate  dry  test  tubes  gently  warm  a  few  crystals  of 
potassium  chlorate,  zinc  sulphate,1  barium  chloride,^  potassium 
sulphate^  potassium  nitrate,  and  alum. 

Record  the  results  in  the  following  tabular  form: 

TABLE 


SUBSTANCE  HEATED 


Is  WATER  DEPOSITED 
IN  COOL  PORTION  OF  TURK  ? 


APPEARANCE  OF  RESIDUE 


&>*, 


-ei 


Do    all   crystalline   substances  contain   water  of  crystallization? 
Illustrate. 


EQUIVALENT  OF  MAGNESIUM 


39 


EXPERIMENT   16    — 
Equivalent  of  Magnesium 

APPARATUS.     Gas-measuring  tube,  50  cc. ;  battery  jar ;  thermometer ; 

barometer. 
MATERIAL.     Magnesium ;     concentrated   hydrochloric   acid ;     thread ; 

water   for  the  battery  jar  that  has  stood  long  enough  to  come  to 

the  room  temperature. 

The  data  for  this  experiment  should  be  tabulated  as  shown  on  page  41. 

Pour  about  5  cc.  of  concentrated  hydrochloric  acid  into  a  gas- 
measuring  tube.     Fill  the  remainder  ot  the  tube  with  water, 
taking  care  not  to  mix  the  acid  and  water ; 
the  heavier  acid  will  remain  at  the  bottom. 

Roll  a  piece  of  magnesium  whose  exact 
weight  is  known  (about  .045  gram),1  into  a 
loose  coil  somewhat  smaller  than  the  inside 
diameter  of  the  tube.  Pass  a  thread  through 
the  loop  of  the  coil,  and  tie  it. 

Put  the  magnesium  into  the  measuring  tube, 
holding  the  thread  so  that  the  magnesium  will 
not  sink.  Close  the  hibe  with  the  thumb, 
and  invert  it  into  a  battery  jar  of  water,  rest- 
ing the  mouth  of  the  tube  against  the  bottom, 
so  that  the  thread  will  be  held.  Allow  the 
magnesium  to  rise  not  quite  to  the  graduation 
in  the  tube  (Figure  16). 

The  heavier  acid  will  flow  down  and  react 
with  the  magnesium. 
What  is  the  gas  that  collects  ?    &*; 


Figure  16. 


From  what  substance  does  it  came  f 

1  Weigh  a  strip  of  magnesium  ribbon  several  meters  in  length.  By  calcula- 
tion, determine  the  length  of  a  piece  that  will  weigh  the  required  amount.  Cut 
off  pieces  of  this  length. 


40  LABORATORY  EXERCISES 

Complete  the  equation  : 


magnesium  -{-  hydrochloric  acid  —  >-         - 

|  hydrogen 
L  chlorine 

+ 


r 

Why  is  this  reaction  termed  a  replacement  ? 


When  the  action  has  ceased  (all  the  metal  being  dissolved), 
adjust  the  levels. 

Read  the  volume  of  hydrogen  obtained  and  record  your  result. 

Record  the  temperature  of  the  liquid  in  the  jar  and  the  barometric 
pressure.  Correct  the  pressure  for  aqueous  tension.  (  Use  the  table 
on  page  240.)  Make  all  calculations  on  page  J^l. 

Reduce  the  volume  of  hydrogen  to  standard  conditions. 

The  weight  of  1000  cc.  (1  liter)  of  hydrogen  is  0.09  g.  Calcu- 
late the  weight  at  standard  conditions  of  the  hydrogen  that  was 
produced  by  the  reaction,  using  the  proportion  : 

corrected  volume      A  nn 
1000  cc.:          ,  ,     ,  ::  0.09  g.  :  x  g. 

of  hydrogen 

This  result  is  the  weight  of  hydrogen  that  is  liberated  by  the 
action  of  your  known  weight  of  magnesium. 

Calculate  how  much  magnesium  would  have  been  necessary  to  liber- 
ate 1  gram  of  hydrogen. 

This  weight  is  called  the  equivalent  of  magnesium. 

The  equivalent  of  any  element  is  the  weight  of  that  element  that  replaces  (or 
combines  with)  i  gram  of  hydrogen. 


EQUIVALENT  OF  MAGNESIUM  41 

TABLE 


Weight  of  magnesium  taken    

W*/g 

Volume  of  hydrogen  obtained      

.    .    .  3£f.$>     cc. 

Temperature       

•  -  -  If.u  °c. 

Barometric  pressure    

.     .    7^J     mm. 

Aqueous  tension     .     .     .     .  '  .    

V.    .    .  -   q     mm. 

Corrected  pressure       

Volume  of  hydrogen  under  standard  conditions    . 

/  J  '7 

;:;:wr 

Weight  of  hydrogen  (calculated)     

...      g. 

Equivalent  of  magnesium  (calculated)      .... 

.  .  .  /,., 

CALCULATIONS 


42  LABORATORY  EXERCISES 

EXPERIMENT   17 

Equivalent  of  Sodium 

APPARATUS.  Metallic  capsule  and  holder  ;  brass  ramrod  to  fit  capsule  ; 
horn  pan  balance  ;  weights  ;  16  oz.  bottle  ;  graduate,  500  cc. ;  pneu- 
matic trough  ;  glass  plate  ;  barometer  ;  thermometer. 

MATERIAL.     Sodium. 

Caution !    Remember  that  the  action  of  sodium  with  water  is  very  violent. 

TJie  data  for  this  experiment  should  be  tabulated  as  indicated  on 
page  43. 

(a)  Weigh  a  metallic  capsule  that  is  clean  and  dry. 
Record  its  weight  in  the  table. 

Nearly  fill  the  capsule,  as  in  Experiment  9,  with  freshly  cut 
sodium  freed  from  any  adhering  crust.     Wipe  off  any  oil  with 
filter  paper.     Weigh  the  capsule  and  contents  quickly. 
Record  the  weight. 

(5)  Fill  the  wide-mouth  bottle  with  water  and  measure  its 
capacity  by  pouring  the  water  into  a  graduate. 
Record  the  volume. 

(c)  Then  fill  the  bottle  with  water  and  invert  it  in  the 
trough.  Place  the  metallic  capsule  in  its  holder.  Raise  the 
bottle  in  the  trough  with  the  left  hand.  Take  the  holder  in 
the  right  hand  and  incline  it  so  that  the  open  end,  of  the  cap- 
sule will  be  downward.  Keeping  the  open  end  downward,  thrust 
the  capsule  under  the  mouth  of  the  bottle.  Control  the  evolu- 
tion of  the  hydrogen  by  slightly  inclining  the  capsule. 

(c?)  When  the  action  ceases,  adjust  the  bottle  so  that  the 
liquid  on  the  inside  is  level  with  that  outside.  Close  the  mouth 
of  the  bottle  with  a  glass  plate,  remove  it  from  the  trough,  and 
set  it  on  the  desk,  mouth  upward.  Pour  the  liquid  now  in  the 
bottle  into  a  graduate. 
Record  its  volume. 


EQUIVALENT  OF  SODIUM  43 

Record  the  temperature  of  the  liquid  in  the  trough  and  the  baromet- 
ric pressure.  Correct  the  pressure  for  aqueous  tension.  {Use  table 
on  page  240.) 

Reduce  the  volume  of  hydrogen  to  standard  conditions.  The 
weight  of  one  liter  (1000  cc.)  of  hydrogen  at  standard  conditions 
is  0.09  gram. 

Calculate  the  iveight  of  hydrogen  evolved.     Then  determine  ivhat 

weight  of  sodium  is  required  to  liberate  1  gram  of  hydrogen. 

This  weight  is  called  the  equivalent  of  sodium. 

The  equivalent  of  any  element  is  the  weight  of  that  element  that  replaces  (or  com- 
bines with)  i  gram  of  hydrogen. 

Make  all  calculations  on  page  44. 

TABLE 


g. 

Weight  of  capsule     

Weight  of  sodium  taken    

Capacity  of  bottle                         

g. 
cc. 

Volume  of  liouid  left  in  the  bottle      ....          . 

cc. 

Volume  of  hydrogen  obtained    . 
Temperature  of  hydrogen                          .                        ... 

cc. 
0  C. 

Barometric  pressure 

mm. 

Aqueous  tension 

mm. 

Corrected  pressure 

mm. 

Volume  of  hydrogen  at  standard  conditions 

cc. 

\Veight  of  the  hydrogen  (calculated) 

Equivalent  of  sodium  (calculated)      

44  LABORATORY  EXERCISES 

CALCULATIONS 


PREPARATION  AND   PROPERTIES   OF  CHLORINE         45 


EXPERIMENT   18 
Preparation  and  Properties  of  Chlorine 

APPARATUS.  Flask  ;  two-hole  rubber  stopper  ;  thistle  tube  ;  four  wide- 
mouth  bottles  (6  oz.),  with  two-hole  rubber  stoppers;  eight  glass 
bends  ;  four  rubber  connectors  ;  ring-  stand  with  large  ring  ;  pan  of 
water  ;  bunsen  burner  ;  four  glass  plates  or  watch  glasses  (Syracuse 
form)  ;  one  hydrogen  generator,  provided  with  jet  tube,  for  the  class. 

MATERIAL.  Concentrated  hydrochloric  acid  ;  manganese  dioxide  ; 
taper  ;  colored  cloth  ;  powdered  antimony^ 

Caution!    Chlorine  is  a  poisonous  gas.    Do  not  inhale  it.    Inhaling  ammonia  or 
alcohol  will  counteract  some  of  its  effects. 

(a)   Preparation. 

Arrange  apparatus  as  in  Figure  17.     Pour  a  small  amount 
of  water  into  the  fourth  bottle.     If  good  hoods  are  available, 


Figure  17. 


Figure  18. 


use  the  apparatus  shown  in  Figure  18.  In  this  case,  the 
solubility  should  be  determined  by  passing  the  gas  into  a  test 
tube  of  water. 

Place  in  the  flask  15  cc.  of  concentrated  hydrochloric  acid  and 


46  LABORATORY  EXERCISES 

add  about  8  grams  of  granular  manganese  dioxide.     Rotate  the 
flask  so  as  to  mix  its  contents,  then  replace  the  stopper. 
Heat  the  water  in  the  dish  under  the  flask  to  boiling. 
Describe  the  action  in  the  generator. 


(£>)   Physical  properties. 

Hold  a  piece  of  white  paper  behind  the  first  bottle. 
What  is  the  color  of  chlorine  ? 

How  can  you  tell  when  the  bottle  is  filled  with  (/as  ?      /  '.' 

/"     '"  '     /  ,  '• 

;\ 


When  the  bottles  are  filled  with  chlorine,  withdraw  the  flame. 
Keep  the  gas  for  use  in  parts  (c),  (d),  and  (e}. 
Is  chlorine  soluble  in  water  ? 
Give  a  reason  for  your  answer.  < 


(c)   Chemical  properties. 

The  instructor  at  this  point  should  introduce  a  jet  of  burning 
hydrogen  into  a  bottle  of  chlorine. 

What  compound  is  formed  when  hydrogen  burns  in  oxygen  ? 

Wliat  is  formed  ivhen  hydrogen  burns  in  chlorine  ? 

cS':<.i^#le*  • 

The  instructor  should  also  sprinkle  a  pinch  of  powdered  anti- 
mony into  a  bottle  of  chlorine. 
Result  ? 


Is  oxygen  necessary  for  combustion  ?     :  i 

Lower  a  lighted  taper  into  a  bottle  of  chlorine.     The  taper 
is  composed  of  compounds  containing  hydrogen  and  carbon. 

Which   of  these   elements  is  liberated  when   the  candle  burns  in 
chlorine  f    ^^%  ^^ 

/" 


PREPARATION  AND  PROPERTIES   OF  CHLORINE         47 


(d)   Bleaching  action  of  chlorine. 

Place  a  piece  of  dry  colored  cloth  in  one  bottle  of  chlorine 
unil  a  piece  of  wet  cloth  in  another.  Cover  the  mouths  of 
the  bottles  with  glass  plates. 

What  must  be  the  condition  of  the  cloth  to  be  bleached  by  chlorine  ? 


Explain  the  bleaching  of  cloth  by  chlorine.     (Class  discussion.) 


(e)  General  questions. 

Hydrochloric  acid  is  a  compound  of  hydrogen  and  chlorine. 
With  what  does  the  oxygen  of  the  manganese  dioxide  combine  f 

^ptertz^  - 

Wliat  is  your  conclusion  as  to  the  chemical  activity  of  chlorine  as 
compared  with  oxygen. 


With  u'hat  elements  does  <-ltlorinp  readily  combine  ? 
/£*4*r2^  ^Z/T 

DRAWING 

' 
/   / 

, 


48  LABORATORY  EXERCISES 

EXPERIMENT   19    - 
Preparation  and  Properties  of  Hydrochloric  Acid 

APPARATUS.  Flask,  250  cc.,  with  stopper  carrying  thistle  tube  and 
delivery  tube  ;  ring-stand  with  one  ring  and  one  clamp  ;  wire  gauze 
with  asbestos  center  ;  bunsen  burner  ;  two  test  tubes  ;  wide-mouth 
bottle  ;  enameled  pan. 

MATERIAL.  Sodium  chloride  ;  sulphuric  acid,  2  to  1  ;  blue  litmus 
paper  ;  magnesium  ;  zinc. 

(#)  Preparation. 

Pour  about  20  cc.  of  sulphuric  acid  (2  to  1)  into  a  flask  sup- 
ported on  a  wire  gauze  on  a  ring-stand,  and  add  about  10  grams 
of  sodium  chloride.  Gently  rotate  the  flask  so  as  to  mix  the 
acid  with  the  chloride.  Close  the  flask  with  a  stopper  carrying 
a  thistle  tube  and  a  delivery  tube  arranged  for  the  collection  of 
gas  in  a  dry  test  tube  by  downward  displacement.  If  neces- 
sary, heat  the  flask  with  a  small  flame. 
Describe  the  action  in  the  generator. 


Of  ivhat  elements  is  hydrogen  chloride  composed  f 

:v  >$/>>.?<••>•..    $'  "J:-  '  •  l^''L 

Which  of  the  original  materials  furnished  the  chlorine  f 
/  ff  >•  / 


Which  furnished  the  hydrogen?    : 

In  this  particular  case,  sulphuric  acid  is  used  because  it  does 
not  vaporize  below  338°,  so  that  none  of  it  passes  off  with  the 
hydrogen  chloride. 

sodium  sulphuric          sodium  hydrogen 

chloride          acid  '    sulphate         chloride 


c^l  sodium 
i  ,(  chlorine 


hydrogen  \ju 

sulphur 

oxygen 


sodium  f/7^.-    -^  J>''"';/ 

sulphur 

oxygen 


Why  is'hydrogen  chloride  collected  by  the  method  used  f 


PROPERTIES  OF  HYDROCHLORIC  ACID 


49 


(5)   Solubility  of  hydrogen  chloride. 

Fill  a  dish  with  water  and  set  it  on  the  table.  Take  the  test 
tube  of  gas  collected  by  the  downward  displacement  of  air, 
close  its  mouth  tightly  with  the  thumb,  invert  the  test  tube,  and 
hold  its  mouth  below  the  surface  of  the  water.  Remove  the 
thumb. 

*&*    *rfn  svw AS***-, 
*ju  ff&f-f 

Explain  why  the  gfos  is  not  collected  over  water. 


Result? 


i 

Close  the  mouth  of  the  test  tube  with  the  thumb  and  remove 
it  from  the  water.  Moisten  a  piece  of  litmus  paper  with  the 
liquid  contained  in  the  test  tube. 

Result? 

Taste  the  liquid. 
Result? 


These  effects  are  typical  of  the  water  solu- 
tion of  acids.  The  solution  in  the  reagent 
bottle  marked  "  hydrochloric  acid "  is  also 
prepared  by  dissolving  hydrogen  chloride  in 
water. 

(c)   Density  of  hydrochloric  acid. 

Pour  not  more  than  10  cc.  of  water  into  a 
wide-mouth  bottle.  Place  the  mouth  of  the 
delivery  tube  within  half  a  centimeter  of, 
but  not  touching,  the  surface  of  the  water  in 
the  bottle  (Figure  19).  Heat  the  flask  with 
a  small  flame,  or  by  a  pan  of  boiling  water, 
for  at  least  ten  minutes.  While  doing  this, 
occasionally  look  through  the  water  in  the  bottle  horizontally. 
Is  the  solution  of  hydrogen  chloride  formed  heavier  or  lighter  than 


Figure  19. 


water?    Explain 
Jr* 


50  LABORATORY  EXERCISES 


Action  of  hydrochloric  acid  with  metals. 

Pour  half  of  the  solution  just  made  into  a  test  tube  and  drop 
into  it  a  strip  of  magnesium.     Bring  a  flame  near  the  mouth  of 
the  tube. 
Results? 

Place  a  piece  of  zinc  in  another  test  tube  and  pour  the  remain- 
ing hydrochloric  acid  upon  it.     Test  the  gas  with  a  flame. 
Results'! 

What  substance  is  liberated  ivhen  hydrochloric  acid  reacts  with 
these  metals  ?  .        /-    /  , 


^.Magnesium  and  zinc  are  elements. 

/     When  hydrochloric  acid  reacts  with  these  metals*  where  does  the 
substance  that  is  liberated  come  from  ?       /%#']'  'g^fa**' 


What  becomes  of  the  metal? 

"' 


What  three  properties  have  been  mentioned  as  characteristic  of 


acids?    ^/t  n^ 

#.ity  -    AwUdt 

'DRAWING 


TEST  FOR  A   CHLORIDE  51 

<T/u.    1  3 
EXPERIMENT   20  ^  jf 

Test  for  a  Chloride 

APPARATUS.     Six  test  tubes  ;  test  tube  rack. 

MATERIAL.     Dilute  hydrochloric  acid  ;    dilute  nitric  acid  ;    solutions  of 

silver  nitrate,  ammonium  hydroxide,  sodium  phosphate,  and  potassium 

oxalate  ;  unknowns. 

(a)  To  a  little  hydrochloric  acid  in  a  test  tube  add  silver 
nitrate  solution.  The  substance  which  separates  out  is  silver 
chloride. 

Complete  the  equation  : 

hydrochloric  acid  +  silver  nitrate  —  >- 


Any  solid  which  thus  separates  out  of  a  clear  liquid  is  known 
as  a  precipitate. 

Describe  the  silver  chloride  precipitate  as  to  color  and  appearance. 


Set  aside  the  tube  containing  the  precipitate. 
(li)  Take  a  little  of  a  solution  of  sodium  phosphate  and  add 
to  it  silver  nitrate  solution. 

Result  f 


Complete  the  equation  : 

^L<r^  -- 
sodium  phosphate  -J-  silver  nitrate 

silver  phosphate 


Describe  the  color  and  appearance  of  the  silver  phosphate. 

^X  » 

Set  the  tube  aside. 

(c)  Take  a  little  of  a  solution  of  potassium  oxalate  and  add 
to  it  silver  nitrate  solution. 
Result  f 


52  LABOEATOEY  EXERCISES 


Complete  the  equation : 

/^','/,*"^X    ' 

potassium  oxalate  -t-  silver  nitrate 
silver  oxalate  + 


Describe  the  color  and  appearance  of  the  precipitate. 


Set  the  tube  aside. 

(d)  Add  nitric  acid  to  each  of  the  three  tubes  containing  the 
three  precipitates. 

What  happens  in  each  case  f 


,  i  M^ 

How  can  you  distinguish  silver  chloride  from   silver  phosphate 
and  form  silver  oxalate  f 

How  can  silver  chloride  be  obtained  from  any  soluble  chloride  ? 


What  two  steps  would  be  necessary  to  distinguish  any  soluble  chloride 
from  any  soluble  phosphate  or  oxalate  ? 


This  procedure  serves  as  a  means  of  distinguishing  chlorides 
from  other  salts. 

Describe  a  test  for  a  chloride. 


TEST  FOR  A   CHLORIDE 


53 


(e)  Make  another  portion  of  silver  chloride.  Let  the  pre- 
cipitate settle,  drain  off  most  of  the  clear  liquid,  and  add 
ammonium  hydroxide. 

Result  f 

' 
A^is     ft*****  '  y 

(/)  Make  still  another  portion  of  silver  chloride  and  see 
what  effect  light  has  on  it.  If  possible,  stand  the  tube  in  the 
direct  sunlight. 

Wliat  further  characteristics  of  silver  chloride  are  shown  in  parts 

(e)  and  (/)  ? 


Apply  to  the  instructor  for  an  "unknown."     Test  it  for 
a  chloride,  writing  the  results  obtained  in  each  step. 

State  your  opinion  as  to  whether  the  unknown  contained  a  chloride, 
and  give  reasons  for  your  belief. 


TABLE 


NUMBER  OF  UNKNOWN 

EFFECT  OF  ADDING 
SILVER  NITRATE 

IF  PRECIPITATE  is  OBTAINED, 
EFFECT  OF  NITRIC  ACID  ON  IT 

54  LABORATORY  EXERCISES 

EXPERIMENT   21 " 
Weight  of  a  Liter  of  Oxygen 

APPARATUS.  Horn  pan  balance  ;  weights ;  test  tube  with  rubber  stopper 
carrying  a  delivery  tube  ;  4  in.  U-tube  with  one-hole  rubber  stoppers 
and  delivery  tube  ;  pneumatic  trough ;  2-liter  bottle  (acid  bottle) ; 
glass  plate ;  graduate  ;  ring-stand  ;  clamp  ;  bunsen  burner. 

MATERIAL.  Well  dried  potassium  chlorate  ;  dry,  powdered  manganese 
dioxide  (C.  P.  quality  gives  a  more  accurate  result);  granulated  cal- 
cium chloride  ;  glass  wool. 

(a)  Arrange  the  apparatus  as  in  diagram  (Figure  20).  The 
U-tube  should  contain  granulated  calcium  chloride. 

Mix  about  6  grams  of  thoroughly  dried  manganese  dioxide 

with  8  grams  of  potassium  chlo- 
rate. (C.  P.  quality  gives  a  more 
accurate  result.) 

Put  the  mixture  into  a  dry  test 
tube,  and  above  the  powder  place 
a  loose  plug  of  glass  wool. 

Tabulate  the  data  as  indicated 
by  the  table  on  page  55. 

(6)   Weigh  to  a  centigram  the 

test  tube  containing  the  mixture,  the  connecting  tube  with  its 
two  stoppers,  and  the  U-tube. 
Record  the  weight  in  the  table. 

Clamp  the  apparatus  in  place,  and  adjust  the  rubber  stopper 
carrying  the  delivery  tube  leading  to  the  pneumatic  trough. 
Collect  the  gas  in  an  acid  bottle  of  about  2  liters'  capacity. 

The  test  tube  should  be  inclined  at  a  slight  angle  so  as  to 
permit  the  spreading  of  the  black  mixture  along  the  tube.  Heat 
with  a  small  flame,  beginning  at  the  top,  and  gradually  working 
downward. 

Carefully  regulate  the  heat  so  that  you  can  always  count  the 
bubbles  of  the  oxygen.  Continue  the  heating  until  the  bottle 
is  nearly  full,  or  as  long  as  time  will  allow. 


WEIGHT  OF  A   LITER   OF  OXYGEN  55 

When  the  oxygen  has  ceased  to  pass  over,  at  once  remove  from 
the  U-tube  the  delivery  tube  with  its  attached  stopper.  Allow 
the  apparatus  to  cool. 

(c)  While  waiting  for  this,  measure  the  volume  of  the  oxygen. 
Lower  the  large  bottle  in  the  trough  so  as  to  adjust  the  water 
levels  to  the  same  height,  close  the  mouth  of  the  bottle  with  a 
stopper  or  a  glass  plate,  and  remove  the  bottle  from  the  trough, 
inverting  it  as  you  do  so. 

Find  the  volume  of  the  oxygen  by  the  amount  of  water 
necessary  to  fill  the  bottle,  pouring  the  water  into  the  bottle 
from  a  graduate. 

Record  in  the  table. 

(d)  When  the  test  tube  has  cooled  until  it  feels  barely  warm 
to  the  hand,  weigh,  as  before,  the  test  tube,  connecting  tube, 
U-tube,  and  contents. 

Record  the  weight. 

The  loss  of  weight  is  the  weight  of  the  oxygen  evolved. 

Record  the  barometric  pressure  and  the  temperature  of  the  water 
in  the  pneumatic  trough. 

This  is  approximately  the  temperature  of  the  gas. 

TABLE 


Weight  of  generating  and  drying  tube  before  heating    .     . 
Weight  of  generating  and  drying  tube  after  heating      .     . 

Weight  of  oxygen  evolved 

Volume  of  oxygen  evolved  under  conditions  of  experiment  £  £<$%$  cc. 

Temperature  of  oxygen /  f   °  C. 

Barometric  pressure -;  tv-  mm. 

Aqueous  tension  (see  table,  p.  240) mm. 

Pressure  of  oxygen       .    ^XV^v-4^ 763  mm' 

Volume  of  oxygen  at  standard  conditions cc. 

Weight  of  one  liter  of  oxygen  at  standard  conditions      .     .  g. 


56  LABORATORY  EXERCISES 

Calculate  the  volume  of  the  oxygen  at  standard  conditions. 

Using  the  weight  of  oxygen  as  found,  calculate,  by  means  of  a 
proportion,  the  weight  of  a  liter  (1000  cc.)  of  oxygen  at  standard 
conditions. 

CALCULATIONS 


BASES  57 

EXPERIMENT   22 
Bases 

APPARATUS.     Evaporating  dish ;  glass  plate,  4x4;  stirring  rod  ;  four 

test  tubes ;  glass  funnel ;  ring- stand  with  one  ring ;  bunsen  burner ; 

wire  gauze  with  asbestos  center. 
MATERIAL.     Metallic  sodium  ;  filter  paper  ;  red  litmus  paper  ;  calcium 

oxide;   sodium  hydroxide  solution,  about  32  g.  to  100  cc.  of  water; 

ammonium  hydroxide  solution,  1  to  5 ;    hydrochloric   acid,  1  to  1  ; 

ferric  chloride  solution,  8  g.  per  100  cc. 

Bases  are  the  chemical  opposites  of  acids.     They  consist  of  a 
metal  united  to  a  hydroxyl  (OH)  group. 

(a)  Very  active  metals  form  bases  by  direct  action  with  water. 

Take  a  freshly  cut  piece  of  sodium  the  size  of  a  pea  and 
completely  remove  the  adhering  oil  with  filter  paper.  Hold 
a  square  of  glass  vertically  (to  protect  the  face)  in  front  of  an 
evaporating  dish  containing  about  10  cc.  of  water.  Place  the 
sodium  on  the  water. 
Describe  the  action. 

,  •'<&%,  A^£>4    rt^w?  :'2/L^  • 

What  gas  is  liberated  f 

Determine  the  action  of  the  solution  011  litmus  and  rub  some 
of  it  between  the  fingers. 
Results  f 

Evaporate  part  of  the  solution  to  dryness.     The  substance 
left  in  the  dish  is  sodium  hydroxide. 
Describe  its  appearance. 

Complete  the  equation : 

Na+  HOJf— ^  NaOH 

Is  sodium  hydroxide  a  soluble  base  ? 


0 


5H  LABORATORY  EXERCISES 

(5)   Some  bases  can  be  prepared  by  action  of  the  oxide  of  the  metal  with 
water. 

Place  a  gram  of  quicklime  (calcium  oxide,  CaO)  in  a  test 
tube  and  add  1  cc.  of  water.  Warm  the  mixture  until  the 
action  starts  ;  remove  the  tube  from  the  flame  and  see  if  there 
is  continued  action  between  the  quicklime  and  the  water.  If 
not,  warm  the  tube  until  an  action  begins  and  continues  without 
the  further  addition  of  heat. 
Describe  the  action.  , 

Mi* 

How  does  the  substance  formed  compare  ivith  the  original  lime  ? 

/ur£  •         '• 


This   new    substance    is    slaked    lime    (calcium   hydroxide, 
Oa(OH)2). 

Write  an  equation  for  its  formation. 

Ca. 


Add  water  to  the  slaked  lime,  shake  thoroughly,  and  allow 
the  solid'-  to  settle.     Pour  off  the  clear  liquid  into  another  test 
tube,  retaining  the  solid  for  part  (d).     Determine  the  action 
of  this  solution  on  litmus. 
Result?  A 


Is  calcium  hydroxide  a  soluble  base  ?      State  reasons  for  your 
'/ answer.  Ct^itf.   '  '£-» 

K.U- 


uwi^tt  •  v/  A-/,-/L.        m  &  *•*'•  f^ 

7  / 

What  common  property  have  the  solutions  of  sodium  hydroxide 

and  calcium  hydroxide  ? 

// 

f    /,-f^'V.A^—     »  /y  .•'     /  . 

This  is  one  of  the  characteristic  properties  of  the  solutions  of 
metallic  hydroxides  (basee^. 


BASES  59 

(c)   Other  bases  can  be  prepared  by  a  process  of  precipitation. 
To  5  cc.  of  a  hot  solution  of  ferric  chloride  add  4  cc.  of  am- 
monium hydroxide. 

,  V  *^AP^jJjArtAL     ^V-i**^  *- 


Result  ?  <<.   ; 


^v^  / 

Complete  the  equation  : 

FeCl3+  3    NH4OH-^Fe(OH)3 


Filter  the  solution  and  thus  obtain  the  ferric  hydroxide  on  a 
filter  paper.  Wash  it  thoroughly,  using  three  separate  portions 
of  water.  Allow  each  portion  of  the  water  to  drain  through 
completely  before  the  next  is  added. 

Transfer  the  washed  precipitate  to  a  test  tube,  add  5  cc.  of 
water,  and  shake  the  mixture  thoroughly.  Allow  the  precipi- 
tate to  settle  and  pour  off  most  of  the  clear  liquid.  This  is  to 
complete  the  washing  of  the  ferric  hydroxide.  Add  5  cc.  of 
water,  shake  the  mixture,  and  determine  its  action  on  litmus. 
Is  there  any  evidence  that  ferric  hydroxide  is  soluble  ? 


Retain  the  contents  of  the  tube  for  part  (6?). 

What  characteristic  must  bases  have  in  order  to  act  on  litmus  ? 

.^vwWxVfe  *^WU*_.  -  <*••• 


Determination  of  the  action  of  bases  with  acids. 
Place  in  one  test  tube  sodium  hydroxide  solution,  in  a  sec- 
ond, some  of  the  solid  calcium  hydroxide  from  part  (£>),  and  in 
a  third,  the  ferric  hydroxide  from  part  (c).  To  each  add  5  cc. 
of  hydrochloric  acid.  Determine  whether  heat  is  produced  in 
each  case. 

Results*^ 


Do  you  observe  any  other  erirlvnces  of  chemical  action  ? 

^t 


60 


LABORATORY  EXERCISES 


Complete  the  equations  : 

NaOH  +  HC1 

Ca(OH),+  HC1 

Fe(OH)3  +  HC1 


TABLE 


NAME  OF  BASE 


SOLUBLE  OB  INSOLUBLE  ACTION  ON  LITMUS 


ALKALIES  61 

/•<*   14 
EXPERIMENT   23 

Alkalies 

APPARATUS.  Six  test  tubes;  two  beakers,  150  cc.  ;  evaporating  dish; 
ring-stand  with  ring  ;  wire  gauze  with  asbestos  center  ;  bunsen 
burner  ;  glass  rod. 

MATERIAL.  Washing  soda  ;  borax  ;  sodium  sulphate  ;  baking  soda  ; 
solution  of  sodium  hydroxide,  10  g.  to  100  cc.;  solution  of  ammo- 
nium hydroxide,  1  to  3  ;  pieces  of  cloth  with  small  grease  spots  of 
butter  ;  cotton  cloth  ;  woolen  cloth  ;  red  litmus  paper. 

The  term  alkali  is  applied  to  any  substance  whose  water  solu- 
tion turns  litmus  blue.  The  soluble  bases  are  strong  alkalies, 
but  solutions  of  many  other  substances  also  produce  the  same 
change  in  the  color  of  litmus. 

(a)   Alkaline  reactions. 

Dissolve  a  little  of  each  of  the  following  substances  in  water, 
and  test  the  action  of  its  solution  on  litmus  :  washing  soda, 
Na2CO3;  borax,  Na2B4O7;  sodium  sulphate,  Na2SO4;  baking 
soda,  NaHCOg. 

Results  in  each  case  f 

S 


J/a   Q  03  ^^        +u  *  . 

/Vft2  £6}  AA+?  +<d  /fco*  "    r/     fa  .  ^ 

Are  any  of  these  substances  bases  f 

Give  reasons  for  your  statement.  /  ^C^^i^t 


Name  those  that  are  alkalies. 

• 


<**,+•*  w 


Why  are  they  alkalies  ? 

v 

Alkalies  which  are  not  bases  produce  their  effect  on  litmus 
because,  on  being  dissolved,  they  react  in  a  slight  degree  with 


62  LABORATORY  EXERCISES 

water,  and  form  a  very  small  quantity  of  base.  The  acid  that 
is  produced  at  the  same  time  is  relatively  much  weaker  than  the 
base. 

Complete  the  equations: 

Na2C03  +  H2()  —+  NaOH  + 


NaHCOg  +  H20  — >-  NaOH  +  / 

{'la 


(7>)   Alkalies  as  solvents  for  grease. 

Put  into  a  beaker  a  piece  of  cotton  cloth,  on  which  a  very 
small  grease  spot  has  been  made  with  a  little  butter.  Add 
sodium  hydroxide  solution,  and  boil  the  contents  for  several 
minutes.  Remove  the  cloth  and  examine  it  to  see  if  the  grease 
spot  has  been  affected. 
Result  f 


Using  a  solution  of  borax  as  the  alkali,  repeat  the  experiment . 
Result  f 


Which  of  the  two  filJfalles  Jias  the  greater  grease-dissolving  power  9 


(<?)   Actions  of  alkalies  on  cotton  and  on  woolen  goods. 

Put  a  small  piece  of  each  kind  of  goods  into  separate  test 
tubes,  add  sodium  hydroxide  solution,  and  boil  the  contents  for 
several  minutes., 
Results  ? 


Which  kind  of  goods  is  the  more  affected  by  the  strong  alkali 


ALKALIES  63 

Testing  alkalies  for  volatility. 

A  volatile  substance  is  one  which  turns  completely  into  a  gas 
at  ordinary  temperatures,  or  with  slight  heating.  Put  5  to  10 
drops  of  sodium  hydroxide  solution  into  an  evaporating  dish, 
and  heat  until  no  liquid  remains. 

Is  there  a  residue? 

Is  sodium  hydroxide  volatile  ? 


In  a  similar  way,  heat  a  few  drops  of  a  solution  of  washing 
soda. 

Is  this  alkali  volatile  ? 


By  a  third  test,  determine  whether  a  solution  of  ammonium 
hydroxide  is  volatile  ?  • 
Result  ? 

If  these  three  alkalies  were  applied  to  clothing,  which  would  evapo- 
rate and  ivhich  would  remain  on  the  cloth 


Which  of  them  would  be  most  desirable  to  use  in  cleaning  a  grease 
spot  or  removing  an  and.  stain  from  clothing  f 

i/i^^  , 

Give  reasons  for  your  answer. 

$          '    '          .* 


64 


LABORATORY  EXERCISES 


EXPERIMENT    24 

Neutralization 

APPARATUS.  Two  test  tubes ;  glass  stirring  rod  ;  porcelain  evaporating 
dish,  3" ;  notched  cork  to  fit  acid  bottles ;  wire  gauze  with  asbestos 
center;  ring- stand  with  one  ring;  bunsen  burner;  glass  plate. 

MATERIAL.  Sodium  hydroxide ;  blue  litmus  paper ;  red  litmus  paper  ; 
hydrochloric  acid,  1  to  10;  potassium  hydroxide;  nitric  acid,  1 
to  10. 

(a)  Put  a  small  piece  of  sodium  hydroxide  (about  half  a 
oranO  into  a  test  tube  half  filled  with  water.  As  soon  as  the 

t5  / 

sodium  hydroxide  has  dis- 
solved, fill  the  tube  with 
water,  •  and  thoroughly  mix 
the  solution  by  pouring  it 
£',,.--''  ,-4  back  and  forth  from  one  test 
tube  to  another  several  times. 
Now  pour  half  of  the  solution 
down  a  glass  stirring  rod  into 
a  porcelain  evaporating  disli 
(Figure  21). 

Lay  a  piece  of  blue  litmus 
paper  and  a  piece  of  red  litmus  paper  on  a  glass  plate.  Touch 
each  kind  of  paper  with  the  end  of  the  stirring  rod  wet  with 

the  solution. 

/  / 

What  change  do  you  observe  ? 

Solutions  producing  such  a  change  are  called   A/tX* 

Take  a  bottle  of  dilute  hydrochloric  acid  and  close  the 
mouth  of  the  bottle  with  a  notched  cork  stopper  as  shown  in 
Figure  22.  Wet  the  end  of  the  glass  stirring  rod  with  the 
dilute  acid,  touch  the  wet  end  to  the  inner  surface  of  the  dish, 
so  that  most  of  the  liquid  runs  off  and  then  touch  each  kind 
of  litmus  paper  with  the  wet  end  of  the  rod. 


Figure  21. 


NEUTRALIZATION 


65 


Result? 


.     '^ 


/s  reaction  is  characteristic  of  all  water  solutions  of 


Add.  the  acid,  a  few  drops  at  a  time,  to  the  solution  of  sodium 
hydroxide  in  the  evaporating  dish.     Stir  the  liquid  thoroughly 
after  each  addition  of  acid,  and,  after  stir- 
ring, touch  a  piece  of  blue  litmus  paper 
with  the  wet  end   of   the   stirring   rod. 
Continue  the  addition  of  acid  until  you 
observe  a  change  in  the  color  of  the  litmus 
paper. 

The  liquid  now  gives  an 
reaction. 


* 


Pour  a  little  of  the  sodium  hydroxide 
solution  remaining  in  the  test  tube  into 
the  evaporating  dish,  stir  the  liquid 
thoroughly,  and  touch  a  piece  of  each 
kind  of  litmus  paper  with  the  wet  end  of 
the  stirring  rod.  If  no  change  in  the 
color  of  the  red  litmus  paper  takes  place,  add  a  little  more  of 
the  sodium  hydroxide  solution. 


Figure  22. 


The,  liquid  now  gives  an 


reaction. 


Now  add  the  acid,  a  drop  at  a  time,  until  the  resulting  liquid 
changes  the  color  of  neither  blue  nor  red  litmus  paper.  The 
solution  is  now  neutral. 

Evaporate  the  liquid  by  setting  the  evaporating  dish  on  a 
wire  gauze  over  the  flame  of  a  bunsen  burner. 
What  is  the  color  of  the  residue  ? 

Taste  the  residue. 
What  is  it  ? 
Complete  the  equation  : 

NaOH  +  HC1  —  >-  HO  + 


66  LABORATORY  EXERCISES 

(£)  Dissolve  about  half  a  gram  of  potassium  hydroxide  in  a 
test  tube  full  of  water,  and,  proceeding  as  in  (a),  neutralize 
the  solution  with  dilute  nitric  acid, 

Evaporate  the  neutral  solution  to  dryness.  The  residue  is 
potassium  nitrate,  KNO3. 

Write  the  equation  for  the  neutralization. 

'  ;  /        '  k  "A  .  I-/  \l  v>-  '-A'-'-- 

'     !/'/^    -4    t-i    '  •  -  i 

Potassium  nitrate  is  called  a  salt,  that  is,  it  is  a  compound 
formed  by  the  combination  of  a  metal  with  an  acid  radical  (an 
acid  minus  its  replaceable  hydrogen). 

What  radical  (group  of  elements  that  tend  to  ding  together  during 
a  chemical  change)  is  present  in  every  base  ? 
What  element  is  contained  in  every  acid  ? 
What  becomes  of  the   characteristic  radical  of  a   base    and   the 

characteristic  element  of  an  acid  during  neutralization  ? 

2^- 

What  becomes  of  the  remainder  of  the  base  and  the   remainder 
of  the  acid  ? 

1 

Complete  the  general  statement  concerning  neutralization  : 
acid  +  base  —  *-  + 

Complete  the  following  equation  used  to  represent  the  dissociation 
of  sodium  hydroxide  dissolved  in  ivater: 
NaOH  -*-  Na+  + 


Which  ,of  these  ions  is  present  in  a  water  solution  of  any  base  ? 

Write  the_  equation^representing  the   dissociation   of  hydrochloric 
acid.  Q,  t  ^  h 

What  ion  is  present  in  a  water  solution  of  any  acid  f 

What  compound  results  from  the  combination  of  the  ion  character- 
istic of  acids  with  the  ion  characteristic  of  bases  f 

Write  the  reversible  equation  for  the  reaction  between  the  metallic 
ion  of  the  base  and  the  negative  ion  of  the  acid. 


CONCENTRATION  OF  A    SOLUTION  BY  TIT  RATION       C7 


EXPERIMENT   25 

•^ 

Determination  of  the  Concentration  of  a  Solution  by  Titration 

APPARATUS.  Two  burettes  ;  beaker  or  Erlenmeyer  flask  ;  stirring  rod  ; 
ring-stand  with  two  clamps. 

MATERIAL.  Solutions  of  hydrochloric  acid  (preferably  fifth-normal, 
made  by  dissolving  17  cc.  of  concentrated  hydrochloric  acid  in  500  cc. 
of  water,  and  then  making  up  the  volume  to  1000  cc.),  sodium  hydrox- 
ide, and  phenolphthalein  (made  by  dissolving  1  gram  of  phenolphthalein 
in  100  cc.  of  50  %  alcohol).  A  normal  solution  of  an  acid  contains 
1  gram  of  replaceable  hydrogen  per  liter.  A  normal  solution  of  a  base 
contains  1 7  grams  of  replaceable  hydroxyl  per  liter. 

Fill  one  burette  above  the  zero  mark  with  a  solution  of  hy- 
drochloric acid  of  known  concentration.  Draw  off  enough  of 
the  acid  to  remove  the  air  bubbles  from  the 
tip  and  bring  the  meniscus  (curved  surface  of 
the  water)  to  the  graduated  portion  of  the 
burette. 

Burettes  are  marked  in  various  ways. 
Notice  on  those  you  have,  whether  each  cubic 
centimeter  is  numbered,  and  whether  the  frac- 
tions are  fifths  or  tenths  of  a  cubic  centimeter. 

In  reading  a  burette,  read  from  the  bottom 
of  the  meniscus,  using  care  to  have  the  eye, 
graduation,  and  lowest  part  of  the  meniscus 
on  the  same  level. 

Similarly,  fill  another  burette  with  the 
sodium  hydroxide  solution  whose  concentra- 
tion is  to  be  determined  and  adjust  the  level 
of  the  liquid.  Fisure  2 

Record  the  readings  of  both  burettes  in  a  table  like  that  given  beloiv. 

Allow  about  10  cc.  of  the  sodium  hydroxide  solution  to  flow 
from  the  burette  into  an  Erlenmeyer  flask  or  into  a  beaker,  and 


68  LABORATORY  EXERCISES 

add  a  drop  or  two  of  some  indicator,  e.g.  a  solution  of  phenol- 
phthalein. 

What  color  is  produced   when  phenolphthalein   is   added  to   an 
alkaline  solution  ?    , 


To  an  acid  solution  ? 


Why  is  phenolphthalein  called  an  indicator  ? 
Jfopf'.*  (i~<f...  w!M*'-'-*^     •''/-     :>•  '~-£  $-*.  C  . 

Allow  the  hydrochloric  acid  to  flow,  a  few  drops  at  a  time, 
into  the  sodium  hydroxide  solution,  stirring  or  shaking  after 
each  addition,  until  the  reddish  tinge  just  disappears.  Now 
add  the  sodium  hydroxide  solution,  a  drop  at  a  time,  until  a 
reddish  tinge  is  produced  ;  then  determine  whether  a  drop  of 
acid  will  make  the  solution  change.  If  it  will  not,  continue  in 
the  manner  indicated  until  a  change  of  color  is  produced  by  a 
drop  or  two  of  either  acid  or  of  base. 

Read  the  burettes  to  tenths  of  a  cubic  centimeter  and  record  the 
final  readings  in  the  table. 

Make  three  separate  determinations,  washing  out  the  flask 
after  each  determination. 

TABLE 


Reading,  acid  burette  (before  neutralization  ) 
Reading,  acid  burette  (when  neutralization  is  complete) 
Volume  of  hydrochloric  acid  used 
Reading,  base  burette  (before  neutralization) 
Reading,  base  burette  (when  neutralization  is  complete) 
Volume  of  sodium  hydroxide  used 

DETERMINATION. 

1 

2 

3 

AVER. 

CONCENTRATION   OF  A   SOLUTION  BY  TIT  RATION       69 

Make  all  calddations  on  the  lower  half  of  the  page. 

From  the  number  of  grams  of  hydrogen  chloride  in  the  standard 
hydrochloric  acid  used,  calculate  the  weight  of  hydrogen  chloride  in 
the  average  volume  of  the  acid  used.  Ans.  g. 

From  the  equation 

NaOH  +  HCl— >- + 

calculate  the  weight  of  the  sodium  hydroxide  needed  to  neutralize  the 
hydrogen  chloride  contained  in  the  average  volume  of  hydrochloric 
acid  used.  Ans.  g. 

From   the   average  volume  of  sodium  hydroxide  used,  calculate 
the  weight  of  sodium  hydroxide   in   1   cc.   of  the   solution  tested. 
9- 


Calculate  the  weight  of  sodium  hydroxide   in  one  liter  of  this 
solution.     Ans.  g. 

Proceeding  as  above,  you  could  now  make  use  of  the  sodium 
hydroxide  solution,  whose  concentration  is  now  known,  to  de- 
termine the  concentration  of  a  solution  of  sulphuric  or  other 
acid.  The  table  and  calculations  would  be  similar  to  those 
already  used. 

CALCULATIONS 


70  LABORATORY  EXERCISES 

EXPERIMENT   26 

Types  of  Chemical  Change. 

Direct  Combination.    Simple  Decomposition. 

APPARATUS.  Asbestos  mat ;  hard  glass  test  tube ;  bunsen  burner ; 
electrolysis  apparatus  (one  for  entire  class)  like  that  shown  in  Figure 
24,  consisting  of  a  U-tube  provided  with  two  side-arm  delivery  tubes, 
and  with  carbon  electrodes ;  crystallizing  dish,  5  in. ;  two  4  in.  test 
tubes ;  forceps. 

MATERIAL.  Iodine;  yellow  phosphorus ;  filter  paper  ;  mercuric  oxide; 
hydrochloric  acid,  concentrated  ;  wooden  splinter  ;  saturated  solution 
of  common  salt. 

Relation  of  energy  to  chemical  action. 

Energy  is  the  ability  to  do  work.  The  more  common  ways 
in  which  it  manifests  itself  are  through  heat,  light,  and  elec- 
tricity. 

Name  chemical  reactions  in  which  these  forms  of  energy  are  con- 
cerned. 


(0)   Direct  combination. 

Put  a  small,  thin  piece  of  yellow  phosphorus  on  a  piece  of 

filter  paper  on  an  asbestos  mat.  Phosphorus  must  be  kept  under  water 
until  the  moment  of  use.  It  takes  fire  easily,  and  its  burns  are  serious.  With 
forceps,  lay  a  crystal  of  iodine  on  the  piece  of  phosphorus. 
Stand  well  back,  as  the  action  is  vigorous. 

Are  phosphorus  and  iodine  elements  or  compounds  f    ' 

Complete  the  equation  : 

_£_  +  I     _^PI3. 

/  • .  •  i  Q  -'L-I/YI  f-  v 

Why  is  the  reaction  called  a  direct  combination  ? 
9J      /  }  * "H     '  *     J     ^      '  *  '  '•">  J 

/  y~-'  i 

Is  energy  liberated  or  absorbed  in  this  reaction  f 
State  reasons  for  your  answer. 


SIMPLE    DECOMPOSITION  71 

Name  three  other  experiments  that  you  have  performed  in  which 
elements  combined  directly  without  continuous  application  of  heat. 


state  in  each  case  whether,  after  the  action  was  once  started,  energy 
ivas  absorbed  or  liberated. 


This  evidence  will  guide  you  in  choosing  a  word  to  insert  in 
the  blank  in  the  statement  of  the  following  important  principle: 
Direct  combinations  take  place  readily  only  when  energy  is 


()   Direct  decompositions. 

Heat  a  little  mercuric  oxide  in  a  hard  glass  test  tube.     Test 
for  oxygen  from  time  to  time. 

1   What  forms  on  the  sides  of  the  tube  ?  [tsl/t^S- 


Write  an  equation  for  the  reaction. 

-»  •  3.  &  +  0^ 

Wtiy  is  the  action  called  a  direct  decomposition 


Stop  heating  the  mercuric  oxide. 
Does  the  action  continue  f 


Is  energy  liberated  or  absorbed  in  this  action  ? 

The  instructor  should  have  in  operation  one  or  more  of  the 
pieces  of  apparatus  like  that  in  Figure  24.     In  this  an  electric 
current  is  passing  through  a  concentrated  solution  of  hydro- 
chloric  acid.     The   gas   that   is   given   off  from  the  anode  is 
collected  over  a  saturated  solution  of  common  salt. 
What  gas  is  given  off  at  the  anode  ? 
At  the  cathode  ? 

' 


72 


LABORATORY  EXERCISES 


Stop  the  flow  of  the  current. 
Does  the  action  continue  ? 

Is   energy    liberated  or  ab- 
sorbed in  this  reaction  ?    . 

Write  an  equation  for  the  re- 
action. 

-U&1  — -*  Ay      x 

Why   is   it   called   a   direct 
decomposition  ?    j:  / 


Figure  24. 


The  evidence  of  these  two  experiments  will  guide  you  in 
choosing  a  word  to  fill  in  the  blank  in  the  statement  of  the  fol- 
lowing principle  : 

In  most  cases  of  direct  decomposition,  energy  is 


SIMPLE  REPLACEMENT  73 

EXPERIMENT   27  - 
Types  of  Chemical  Change.    Simple  Replacement 

APPARATUS.     Two  test  tubes. 

MATERIAL.      Zinc  ;  dilute  hydrochloric  acid,  1  to  4  ;  fine  iron  filings  ; 
saturated  solution  of  copper  sulphate. 

(a)  Place  a  piece  of  zinc  in  a  test  tube  and  add  5  cc.  of 
dilute  hydrochloric  acid.  After  the  action  has  continued  for 
several  minutes,  feel  the  test  tube. 

Is  energy  liberated  or  absorbed  in  the  reaction  9 

Write  an  equation  for  the  reaction. 

L  -uJ^t-e-  —  »  .  ^7 

^s^  ^^  C^^ 

Why  is  this  said  to  be  a  case  of  simple  replacement  9 


(5)  To  8  cc.  of  a  saturated  solution  of  copper  sulphate  con- 
tained in  a  test  tube,  add  2  cc.  of  fine  iron  filings.  Close  the 
mouth  of  the  tube  with  the  thumb  and  shake  the  solution  back 
and  forth  several  times.  After  the  action  has  continued  a  few 
minutes,  feel  the  test  tube. 

Is  energy  liberated  or  absorbed  in  the  reaction  9 

Allow  the  test  tube  to  stand  for  several  minutes. 

What  change  takes  place  in  the  color  of  the  solution  ?  J-fstF 


What  change  takes  place  in  the^  appearance  of  the  solid  9 
s£/»**>  SutcL  .   *&'ristAJ,  &    & 


Complete  the  equation: 
CuS04  +  Fe 


Why  is  this  called  o,£ase  of  simple,  replacement  9 


From  the  evidence  of  the  two  experiments,  choose  a  word  to 
fill  in  the  blank  in  the  following  statement  of  an  important 
principle  : 

When  simple  replacements  take  place,  energy  is  _  -*_. 


74 


LABORATORY  EXERCISES 


Heats  of  formation. 

In  the  case  of  most  compounds,  energy  is  liberated  when  the 
elements  unite  to  form  the  compound.  The  amount  of  energy 
is  known  as  the  heat  of  formation.  In  the  case  of  certain  com- 
pounds energy  must  be  furnished,  as  it  is  absorbed  when  the 
compound  is  formed.  In  such  a  case,  the  substance  is  said  to 
have  a  negative  heat  of  formation.  The  amount  of  energy  is 
expressed  in  calories  of  heat.  A  calorie  is  the  amount  of  heat 
necessary  to  warm  one  gram  of  water  one  degree  centigrade. 
The  heat  of  formation  is  the  number  of  calories  of  heat  absorbed 
or  liberated  during  the  formation  of  one  gram-molecule  (a 
weight  in  grams  equal  to  the  molecular  weight)  of  a  compound 
from  its  elements. 

The  following  table  gives  the  heats  of  formation  of  certain 
compounds.  TABLE 

HEATS  OF  FORMATION  OF  CERTAIN  COMPOUNDS 


CALORIES 

CALORIES 

Calcium  aluminum  silicate 

1195,550 

Magnesium  (chloride)  (dil. 

Calcium  carbide 

-6250 

sol.) 

187100 

Carbon  disulphide 

-19000 

Magnesium    sulphate    (dil. 

Copper    (cupric)  chloride 

sol.) 

321100 

(dil.  sol.) 

62500 

Mercuric  chloride  (dil.  sol.) 

50300 

Copper  (cupric)  sulphate 

Mercuric  cyanide 

-62500 

(dil.  sol.) 

197500 

Nitrous  oxide 

-20600 

Hydrogen  chloride 

22000 

Nitric  oxide 

-21600 

Hydrogen  bromide 

8400 

Phosphorus  pentoxide 

369400 

Hydrogen  iodide 

-7000 

Potassium  iodide  (dil.  sol.) 

81800 

Hydrogen  sulphide 

4800 

Potassium  bromide  (  dil.  sol.) 

90400 

Iron  carbide 

8460 

Potassium  chlorate 

93800 

Iron  (ferrous)  chloride 

Potassium    chloride    (dil. 

(dil.  sol.) 

100100 

sol.) 

101200 

Iron  (ferric)  chloride 

Silicon  carbide 

1963 

(dil.  sol.) 

255700 

Silver  oxide 

7000 

Iron  (ferrous)  sulphate 

Sodium  chloride  (dil.  sol.) 

96900 

(dil.  sol.) 

234900 

Sodium  iodide  (dil.  sol.) 

70400 

Iron  (ferric)  sulphate 

Zinc  chloride  (dil.  sol.) 

113300 

(dil.  sol.) 

650500 

Zinc  cyanide 

-27900 

DIRECT  COMBINATION  75 

Bearing  in  mind  the  first  principle  stated  in  Experiment  26,  pick 
out  from  the  table  five  compounds  that  could  easily  be  formed  by 
direct  combination. 

*t 
rame  three  that  could  not  be  firmed  Easily  by  direct  combination. 


In  decomposing  a  compound,  exactly  as  much  energy  must 
be  furnished  as  is  liberated  when  the  compound  is  formed. 

Bearing  this  fact  in  mind,  and  also  the  second  principle  stated  in 
Experiment  26,  name  five  compounds  that  it  would  be  diffictdt  to 
decompose.  -/  /  , 


Also  name  five  that  would  easily  be  decomposed.          rzJ- 

& 

would  decompose  with  liberation  of  energy. 


. 

decide  whether  or  not  replacement  actions  will  take  place, 
compare  the  heats  of  formation  of  the  original  compound  with 
that  of  the  one  that  might  be  formed  in  the  reaction. 

What  principle  will,  then,  guide  you  in  making  your  decision  ? 


Of  the  following  equations,  complete  those  whicli  you  think  will 
actually  occur  ;  in  the  other  cases  write  the  ivords  "no  reaction." 


ZriCl2  4-  Cu 
^xKBr     +CJ2 
NaCl    4-1 


CuCl2  +  Mg  —  ^     / 
HgCl2  4-  Cu  —  ^_ 


. 
Verify  your  conclusions  in  one  or  two  cases. 


76  LABORATORY  EXERCISES 

•1 

.EXPERIMENT   28 

NWy 

Types  of  Chemical  Action.     Double  Decompositions. 

APPARATUS.     Six  test  tubes. 

MATERIAL.  Solutions  of  barium  nitrate,  lead  nitrate,  silver  nitrate, 
ammonium  chloride,  sodium  sulphate,  sodium  chloride,  copper 
sulphate  (all  approximately  N/5),  sodium  hydroxide  (1  to  10), 
dilute  hydrochloric  acid  (1  to  3);  solid  sodium  sulphite,  copper  sul- 
phate, sodium  carbonate,  ferrous  sulphide,  ammonium  chloride. 

(a)   Effect  of  insolubility  of  one  of  the  products. 

To  5  cc.   of  a  solution  of  barium  nitrate,  add  a  little  of  a 
solution  of  sodium  sulphate. 

What  evidence  is  there  that  chemical  action  has  occurred  ? 

Allow  the    tube    to   stand  a  few   minutes.     The    substance 
that  settles  is  barium  sulphate. 

Show  by  completing  the  following  equations  what  ions  are  formed 
by  barium  nitrate  and  by  sodium  sulphate  : 

A'    :   -y    \     +  /_ 


•M-J.  $o  -^  —  />  ">  -jA'"Q  i 

i>anOw1  -  >  _  -t-     ,:>  i    ..      •] 

l^ 

Explain  why  these  actions  are  reversible  reactions. 


Show  by  an  equation  how  barium  sulphate  results  on  mixing 


two  .solutions. 

f>C4  •—  ' 

In  this  case,  is  there  equilibrium,  or  an  action  that  goes  to  an  end? 

^-^  4i  h  ;(-  -*fi-  -• 

Explain  why  such  an  action  is  called  a  double  decomposition. 

- 


DOUBLE  DECOMPOSITION 


11 


The  remaining  parts  of  the  experiment  are  intended  to  illus- 
trate the  conditions  under  which,  on  mixing  two  substances 
that  ionize,  we  get  either  an  equilibrium  or  an  action  that  goes 
to  an  end. 

Try  the  action  between  solutions  of  the  substances  paired  in 
the  following  table ;  record  your  observations  of  the  results  in 
column  2 ;  the  information  needed  for  column  5  may  be  found 
in  the  table  on  page  236 ;  fill  in  the  last  column  after  studying 
the  rest  of  the  table  as  a  whole : 

TABLE 


SUBSTANCES  WHOSE 

SOLUTIONS  ABE 

MIXED 


DOES  ACTION- 

GO   TO  AN 

END  OB 
REMAIN  IN 
EQUILIBRIUM 


PR°08DU™          REA8°*    F°E 
SO^BLE^R    CA8CT'°^\ 

INSOLUBLE  ?  1^™^? 
(See  p.  236)  j  TO  AN  END) 


2-\) 


}s  +  NaCl 
Pb(X03)2 
CuSO4  +  NaOH 


Pb(N03)2  +  NaCl- 


CuS04+NH4Cl 


Complete,  the  following  sentence :  A  double  decomposition  will  go  to 
an  end  if  one  of  the  possible  products  is  _  _. 

(&)   Effect  of  volatility  of  one  of  the  products. 

In  these  experiments,  use  the  first-named  substance  as  a  solid. 
Fill  the  curved  bottom  of  the  tube  with  the  substance  and  add 


78 


LABORATORY  EXERCISES 


about  2  or  3  cc.  of  the  second  compound.     Fill  in  the  table  as  in 
part  (a).     Information  for  column  5  may  be  found  on  page  237. 


TABLE 


SUBSTANCES  USED 

DOES  THE 
ACTION  Go 

TO   AN    EN  I)  ? 

IONS  THAT 
COULD  BE 
FORMED 

PKODUCTS 
POSSIBLE 
BY  NEW  COM- 
BINATION 

OF  IONS 

POSSIBLE 
PRODUCTS 
VOLATILE  ? 
(See  p.  237) 

KEASON  IN 
CASE  ACTION 
GOES  TO  AN 
END 

Na2S03  +  HC1 

W- 

bfrsp 

(a).' 
(ft)^>1 

(«)S.^ 

/lST  '-  ?l  -i  '-'•• 

CuS04  +  HC1 

*p*l' 

£^/jv 

(a) 

(a) 

*"/  ,  •  .  «  <—  , 

Na2C03  +  HC1 

/p/lSs^i,     . 

$ff£ 

(a) 

(ft) 

/-/  .;:>y^  //i 

FeS  +  HC1 

,                    N, 

jf^.  t/i^f— 
C'^\.n  -• 

|"| 

(a) 
(ft) 

(ft)   ^ 

\  f  *  "  it  *  'i 

: 

M*w_ 

3   '  -' 

(ft) 

Complete  the  following  sentence :  Double  decompositions  go  to  an 
end  if  one  of  the  possible  products  is    ;.*-/• /  . 

It  will  be  seen  from  these  experiments  that  a  double  decom- 
position goes  to  an  end  if  one  of  the  products  leaves  the  field  of 
action.  If  water  is  found  in  a  double  decomposition,  it  also 
leaves  the  field  of  action,  because  water  does  not  form  ions 
readily,  and  therefore  is  as  much  out  of  the  action  as  if  it  were 
insoluble  or  volatile. 

Explain  tvhy  a  reaction  between  a  base  and  an  acid  goes  to  an  end. 

ff  c<*s.*t±  rj6u.  c/t?+ 

xW&i.    ^  JwvJu'^    n 


SALTS   THAT  ARE  NOT  NEUTRAL  79 

EXPERIMENT   29 
Salts  that  are  not  Neutral. 

APPARATUS.     Two  test  tubes. 

MATERIAL.  Sodium  carbonate  ;  copper  sulphate  ;  ferric  chloride  ; 
dilute  solutions  'of  aluminum  sulphate,  potassium  chToncleT  borax. 
potassium  nitrate,  zinc  sulpnatgj.  and  ammonium  sulphkte-;  red  and 
blue  litmus  papers.  ^X^fW^^fL, 

(a)  Fill  the  curved  portion  of  a  test  tube  with  powdered 
sodium  carbonate,  Na2CO3.  Add  water  till  the  tube  is  two 
thirds  full  and  shake  it  until  the  sodium  carbonate  is  dis- 
solved. Into  the  solution  dip  a  strip  of  blue  litmus  and  a 
strip  of  red  litmus  paper. 

Eecord  the  remit  in  the  tabular  form  given  on  page  81. 

Water  is  very  slightly  dissociated  into  its  ions  according  to 
the  equation: 


Write  the  equation  for  the  dissociation^of  sodium  carbonate. 

-j/^e<%   -*  ^wttGTJy  -     \  i^~ 

What  four~7cinds  of  ions  are  present  in  the  solution  ? 
Complete  the  following  equilibria  : 

^±:_          :'3 

- 


Carbonic  acid  has  only  a  slight  tendency  to  ionize,  while 
sodium  hydroxide  ionizes  in  much  greater  degree.  Therefore 
the  first  of  these  two  actions  tends  to  remove  from  the  solu- 
tion the  H+  ions  of  the  water  in  greater  degree  than  the  second 
tends  to  remove  the  OH~  ions. 

Which  of  these  two  ions  tends  to  remain  in  excess  f    ^L  0/r" 
How  does  this  explain  the  action  of  sodium  carbonate  solution  on 
litmus  ? 


80  LABORATORY  EXERCISES 

The  practical  effect  of  dissolving  sodium  carbonate  in  water 
is  to  form,  in  slight  degree,  undissociated  carbonic  acid  and  dis- 
sociated sodium  hydroxide. 

Write  an  equation  showing  this. 

•  -f     /*/. 


Of  what  process  is  the  equation  the  reverse  f   ( 
Complete  the  statement : 


Sodium   carbonate   is    formed   by  neutralizing  a.   /^ 

(sfro^ig.or  weak) 

acid  with  a  _  X^v^''^?  base.     Such  a  salt  gives  an   fyjZ/i 

(strong  or  weak) 

reaction  in  water  solution. 

Similarly  test  a  solution  of  sodium  tetraborate  (borax)  with 
the  litmus  papers. 

Record  the  results  in  your  table. 

Why  would  you  expect  sodium  tetraborate  to  give  such  a  reaction  ? 


(6)  In  a  similar  manlier  prepare  solutions  of  copper  sulphate 
and  ferric  chloride,  FeCl8.     Test  each  with  red  and  blue  litmus. 
Record  the  results  in  your  table. 

In  each  case,  name  the  base  formed  that   has   little   tendency   to 
dissociate  again. 

Write  the  equation  for  the  formation  of  each  of  these  two  bases  from 
their  ions. 


What  ion  is  responsible  for  the  litmus  reaction  obtained? 

Write  the  equations  showing  the  combination  of  this  ion  with  the  non- 
metallic  ion  of  the  two  salts. 


Write  the  equation  showing  the  practical  effect  of  dissolving  copper 
sulphate  in  water. 


SALTS    THAT  ARE  NOT  NEUTRAL 


81 


Write  a  similar  equation  for  the  dissolving  of  the  ferric  chloride. 
Of  what  process  is  the  action  in  each  case  the  reverse  ? 

Complete  the  statement: 
Salts  with  an  acid  reaction  ,  are  formed  by  neutralizing  a 

uci<l  with  a  ...  base. 


(strong  or  w^ftk) 




(strong  or  weak) 


(<?)  Aluminum  hydroxide  and  zinc  hydroxide  are  weak  bases. 
Hydrosulphuric  acid,  H2S,  and  tetraboric  acid  are  weak  acids. 

Make  a  prediction  as  to  the  effect  on  litmus  to  be  expected 
from  solutions  of  each  of  the  following  salts,  —  aluminum  sul- 
phate, potassium  chloride,  potassium  nitrate,  zinc  sulphate,  and 
ammonium  sulphide.  Test  your  predictions  by  the  use- of  lit- 
mus with  a  solution  of  each. 

Record  the  results  in  your  tabular  form. 


Complete  : 

weak  acid    4-  strong  base 
strong  acid  +  weak  base 
strong  acid  -f-  strong  base 


salt  with  '; ;:  .* 
salt  with  ,;.^ 
salt  with .  toM. 


',g,  reaction, 

-v    reaction, 

/>  j.  reaction. 


SALT 

ACTION  WITH  ELITE  LITMUS 

ACTIOX  WITH  RED  LITMFS 

Sodium  carbonate 

/^^fe^- 

Copper  sulphate 

/iSr^v   Ct£*^ 

$'    oL 

Ferric  chloride 

&uA*t</  JW*™ 

ty.fatj^ftt  ' 

Aluminum  sulphate 
Potassium  chloride 

,JA*& 

Sodium  tetraborate 

&AAhA*4 

Potassium  nitrate 

^    , 

u,'l/i^JL 

' 

Zinc  sulphate 

\Jt>  tysJW*  At**™ 

fit   Q&Urt- 

Ammonium  sulpMde 

H~ 

LABORATORY  EXERCISES 


82 


EXPERIMENT   30 
Flame  Tests 

APPARATUS.  Bunsen  burner  ;  three  cobalt  glass  plates.  Each  solution 
should  be  contained  in  a  small  bottle  or  vial  with  a  cork  stopper, 
through  which  passes  a  glass  tube  carrying  a  platinum,  iron,  or 
nichrome  wire. 

MATERIAL.     Solutions  of  salts  of  lithium,  sodium,  potassium,  calcium, 
strontium,   and    barium  ;    mixed    solutions 
of  sodium  and  potassium  salts  ;  unknowns. 


(a)  Test  salts  of  lithium,  sodium,  po- 
tassium, calcium,  strontium,  and  barium. 
Hold  one  platinum  wire  at  a  time  in 
the  hot  outer  portion  of  a  bunsen  flame 
(Figure  25).  Observe  the  color  of  the 
flame  in  each  case.  Record  result  in 
tabular  form.  Be  careful  to  replace  each 
wire  in  its  special  bottle. 

TABLE    (PART  a) 


Figure  25. 


SOLUTION 

FORMULA 

COLOR  OF  FLAME 

• 

The  characteristic  coloration  of  the  flame  in  each  case  is  due 
to  the  vapor  of  the  metal  contained  in  the  compound. 

(5)  Observe  the  color  of  a  sodium  flame  through  three  thick- 
nesses, of  cobalt  glass.  In  a  similar  way  examine  the  potassium 
flame  through  the  cobalt  glass. 


FLAME  TESTS  83 

Record  the  result  of  each  flame  test  in  tabular  form  as  indicated 
below. 

Can  you  see  the  sodium  Jiame  through  the  cobalt  glass  1 
What  is  the  effect  of  the  cobalt  glass  on  the  potassium  fame  f 

Take  a  solution  of  a  mixture  of  sodium  and  potassium  salts, 
and,  without  using  the  cobalt  glass,  note  the  flame  color. 
Why  are  not  both  the  characteristic  colors  seen  ? 


Use  the  cobalt  glass  with  the  mixed  solution  and  find  which 
flame  can  be  recognized. 

What  is  the  use  of  the  cobalt  glass  in  making  flame  tests  of  mixtures 
of  sodium  and  potassium  salts  ? 

What  use  might  be  made  of  the  flame  tests  in  analytical  work  f 
TABLE  (PART  6) 


SOLUTION 

COLOB  —  NAKED  EYE 

COLOR  —  COBALT  GLASS 

(<?)  Test  an  unknown  salt  obtained  from  the  instructor. 
When  in  doubt  regarding  the  unknown,  verify  your  conclusion 
by  placing  the  wire  dipped  in  the  unknown  in  one  side  of  the 
flame,  and,  in  the  other  side,  a  wire  dipped  in  a  solution  of  a 
salt  of  the  metal  you  think  is  present. 

Record  the  resulting  color,  and  state  the  metal  present. 

Have  your  conclusion  checked  by  the  instructor. 


84  LABORATORY  EXERCISES 

EXPERIMENT  31 
Preparation  of  an  Acid  Salt 

APPARATUS.  Graduate,  50  cc.  ;  two  beakers  ;  stirring  rod  ;  ring-stand 
with  large  ring  ;  wire  gauze  with  asbestos  center  ;  bunsen  burner. 

MATERIAL.  Solutions  of  sulphuric  acid  (1  to  5),  and  potassium  hydrox- 
ide (200  grams  to  the  liter)  ;  litmus  paper. 

(a)  Take  25  cc.  of  dilute  sulphuric  acid  and  neutralize   it 
with  potassium  hydroxide  solution. 
Write  the  equation. 


Evaporate  one  third  of  the  water  in  the  neutral  solution  and 
set  the  remainder  aside  to  crystallize. 

(5)  In  another  beaker  again  neutralize  25  cc.  of  dilute  sul- 
phuric acid  with  potassium  hydroxide.  Add  to  this  neutral 
solution  another  25  cc.  of  sulphuric  acid.  Evaporate  the  solu- 
tion to  one  third  of  the  volume  and  set  it  aside  to  crystallize. 

Compare  the  crystals  obtained  with  those  obtained  in  part 
(a)  as  to  size  and  general  form. 

'Do  they  appear  to  be  crystals  of  the  same  substance  ? 

There  are  two  potassium  sulphates  :  normal  potassium  sul- 
phate, K2SO4,  and  acid  potassium  sulphate,  KHSO4.    - 
Which  one  was  formed  in  part  (a)?     f[      N 

Write  the  equation  for  the  formation  of  the,  other  in  part  (6). 

/  .  •    '    j 

Why  is  this  called  an  acid  salt? 


PREPARATION  OF  SODIUM  CARBONATE  85 

EXPERIMENT   32  - 
Preparation  of  Sodium  Carbonate 

APPARATUS.     Two  test  tubes,  one  provided  with  a  one-hole  stopper  and 

a  delivery  tube  ;  ring-stand  ;  clamp  ;  bunsen  burner. 
MATERIAL.     Limewater ;  sodium  bicarbonate.  £  tyfc  ft    £,  (y-     -> 

Place  about  two  grams  of  sodium  bicarbonate  in  a  test  tube 
provided  with  a  stopper  and  a  delivery  tube  that  leads  into  a 
test  tube  containing  limewater,  Ca(OH)2.+  ' 

Heat  the  bicarbonate  without  using  sufficient  heat  to  color 
the  flame  yellow. 

What  collects  on  the  inner  ivatt  of  the  test  fubgt       /r*     U 

j,  -*  C  £4+  KJ  v  m^^ .  &->  +- 

What  produced  the  change  iiYthe  limewater?    fy 

The  solid  left  in  the  test  tube  is  sodium  carbonate.    A/Qjo  0  9 

How  does  the  taste  of  the  sodium  carbonate  compare  with  fKat  of 
the  sodium  bicarbonate? 

• 

Complete  the  equations : 
H  NaHCO3  (heated)  — >-  Na2CO3  + 
Ca(OH)2  +  CO2  — ^  CaCO3  + 


86  LABORATORY  EXERCISES 

&    ^ 
EXPERIMENT   33 

U| 

Determination  of  Water  of  Crystallization 

v 

APPARATUS.     Ring-stand  with  two  rings  ;  pipe-stem  triangle  ;  porcelain 

crucible  ;  horn  pan  balance  ;  weights  ;  bunsen  burner. 
MATERIAL.     Crystallized  barium  chloride.. 

Barium  chloride  is  the  salt  selected  for  this  determination, 
because  it  is  easily  obtained  pure  and  is  neither  efflorescent  nor 
deliquescent. 

Weigh  a  porcelain  crucible  on  the  balance.  Then  put  into 
the  crucible  about  two  grams  of  crystallized  barium  chloride, 
and  weigh  carefully  the  crucible  and  its  contents. 

Record  all  iveights  in  a  tabular  form  like  that  given  on  page  S7. 

Support  the  crucible  on  a  pipe-stem  triangle  so  adjusted  in 
height  that  the  bottom  of  the  crucible  is  a  short  distance  above 
the  top  of  the  inner  cone  of  the  bunsen  flame.  Heat  the  cru- 
cible very  gently  at  first.  Too  rapid  heating  may  cause  the 
water  of  crystallization  to  be  driven  off  explosively,  carrying 
along  with  it  some  of  the  salt.  Gradually  heat  the  crucible  to 
the  full  intensity  of  the  flame. 

After  fifteen  minutes  of  this  strong  heating,  slowly  cool  the 
crucible,  and  weigh  the  crucible  and  its  contents. 
Record  the  weight. 

Repeat  the  heating  and  weigh  again.  Continue  this  process 
until  you  get  two  successive  weighings  with  the  same  result. 
This  is  called  "heating  to  constant  weight." 

What  does  this  constant  weight  show  about  the  water  of  crystalliza- 


tionf 


From  your  data  in  the  table  ascertain  (1)  the  weight  of  the  crystal- 
lized barium  chloride,  (%}  the  weight  of  the  anhydrous  barium  chloride 
left  after  heating. 


DETERMINATION   OF   WATER   OF  CRYSTALLIZATION      87 

The  "  anhydrous  "  salt  is  the  crystallized  salt  minus  its  water 
of  crystallization. 

You  know  the  weight  in  grams  of  two  substances,  crystallized 
barium  chloride  and  anhydrous  barium  chloride.  These  weights 
are  in  the  same  ratio  as  the  molecular  weights  of  these  sub- 
stances. 

Using  the  values  given  in  the  table  of  atomic  weights  (page  234), 
calculate  the  molecular  weight  of  anhydrous  barium  chloride±JBajQl2. 

Make  all  calculations  on  page  88. 

Employing  the  three  quantities  that  you  now  know,  and  representing 
the  molecular  weight  of  crystallized  barium  chloride  by  x,  form  a  pro- 
portion in  which,  the  weights  that  you  obtained  by  the  balance  have 
the  same  ratio  as  the  molecular  iveights  of  the  substances  weighed. 

Solve  the  proportion  in  the  space  marked  "  Calculations"  page  88. 
Find  by  subtraction  the  part  of  the  molecular  weight  of  the  crystal- 
lized salt  that  is  water. 

How  many  molecules  of  water  does  this  weight  represent? 
Write  the  formula  of  crystallized  barium  chloride. 


.  Calculate  the  percent  of  water  of  crystallization  in  crystallized 
barium  chloride.   J~%  f 

TABLE 


Weight  of  crucible  +  crystallized  barium  chloride  ... 

Weight  of  crucible  empty 

Weight  of  crystallized  barium  chloride  ....... 

Weight  of  crucible  +  barium  chloride  after  Jirst  heating  . 

Weight  of  crucible  +  barium  chloride  after  second  heating 

Weight  of  crucible  empty 

Weight  of  anhydrous  barium  chloride 

Molecular  weight  of  crystallized  barium  chloride  . 

Molecular  weight  of  anhydrous  barium  chloride 

Molecular  weight  of  water  in  crystallized  barium  chloride 

Formula  of  crystallized  barium  chloride 


88  LABORATORY  EXERCISES 


CALCULATIONS 


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FORMS  OF  SULPHUR 


89 


EXPERIMENT  34 
Forms  of  Sulphur 

APPARATUS.  Two  test  tubes  ;  watch  glass,  2|"  ;  small  iron  clamp  for 
use  as  a  test  tube  holder ;  bunsen  burner ;  magnifying  glass ;  pan 
of  water. 

MATERIAL.     Roll  sulphur ;  carbon  disulphide ;  filter  paper,  4"  in  diameter. 

(a)  Caution !    Carbon  disulphide  is  a  volatile  liquid  that  takes  fire  easily.    It 
should  never  be  used  near  a  flame. 

Pour  5  cc.  of  carbon  disulphide  into  a   test   tube.     Add  a 
piece  of  roll  sulphur  the  size  of  a  pea  and  shake  the  tube. 

Pour  the  clear  liquid  into  a  watch  glass,  and  set  it  aside  to 
evaporate  in  a  part  of  the  laboratory  some  distance  from  a 
flame.  Using  a  magnifying  glass,  examine  the 
crystals  of  sulphur. 

In  the  square  provided  for  the  purpose  make  a 
drawing  of  a  crystal  having  a  symmetrical  form. 

You  have  recrystallized  roll  sulphur  under 
conditions  that  yield  separate  crystals.  Sulphur 
that  crystallizes  as  you  have  just  observed  is 
called  rhombic  sulphur. 

(b)  Fold  a  piece  of  filter  paper  as  you  would 
to  fit  a  funnel,  and  lay  it  aside  for  future  use. 
Also,  have  a  dish  of  water  ready  for  use. 

Half   fill   a   test   tube  with  small   pieces   of 
roll  sulphur.     Carefully  melt  the   sulphur  by 
holding  the  tube  in  an  inclined  position  about 
four  inches  above  a  small  flame  (Figure  26).     Rotate  the  tube 
slowly  while  the  melting  proceeds. 

What  is  the  color  and  consistency  of  the  first  portion  of  liquid 

obtained  9 


I 

1 


Figure  26. 


90 


LABORATORY  EXERCISES 


This  color  should  be  retained  during  the  melting  of  all  of  the 
sulphur.     The  color  should  at  no  time  be  darker  than  a  light 

amber. 

Holding  the  folded  filter 
paper  by  the  edge,  pour  the 
melted  sulphur  into  it  (Figure 
27).  As  soon  as  crystals  have 
formed  from  the  edge  to  the 
center  of  the  surface,  pour 
into  the  water  in  the  pan  that 

part  of  the  sulphur  that  is  still  in  a   melted  condition.     Im- 
mediately unfold  the  filter  paper. 

Make  a  drawing  of  one  of  the  more  perfect  crystals  as  it  is  seen 
under  a  microscope. 

This  form  of  sulphur  is  known  as  prismatic  sulphur. 
Keep  some  of  the  crystals  for  a  few  days  and  then  examine 
them. 

What  changes  do  you  observe  ? 


RHOMBIC  SULPHUI 


PRISMATIC  SULPHUR 


(c)  Half  fill  a  test  tube  with  small  pieces  of  roll  sulphur,  and, 
holding  the  test  tube  with  a  small  iron  clamp,  raise  the  tempera- 
ture of  the  sulphur  until  it  commences  to  boil.  Meanwhile,  tip 
the  tube  slightly  from  time  to  time  and  note  the  important 
changes  that  take  place  in  the  color  and  consistency  (degree  of 
fluidity)  of  the  sulphur. 


FORMS  OF  SULPHUR 


91 


What  changes  in  the  color  and  consistency  of  the  sulphur  did  you 
note  from  the  time  it  melted  until  it  commenced  to  boil  f 

!*SL, 


f  ' 


In  the  next  operation  the  sulphur  will  probably  take  fire. 
Do  not  jump.  The  sulphur  will  burn  quietly.  Do  not  spill  it 
on  the  desk.  Pour  the  boiling 
sulphur  slowly  into  cold  water, 
keeping  the  mouth  of  the  tube 
moving  in  a  circle  so  that  a  thread 
of  sulphur  will  form  in  the  water 
(Figure  28).  Examine  the  thread 
of  sulphur.  It  is  the  plastic 
modification  of  sulphur. 

What  color  is  it 


Figure  28. 


Is  it  hard  or  soft  ? 
?fi  - 

Elastic  or  brittle  f 

' 

Keep  it  for  several  days  and  note  any  change  in  properties. 
Results? 


92  LABORATORY  EXERCISES 

EXPERIMENT    35 
Preparation  of  Metallic  Sulphides 

APPARATUS.  Test  tube ;  ring-stand  with  one  ring ;  wire  gauze  with 
asbestos  center  ;  bunsen  burner  ;  small  iron  clamp. 

MATERIAL.  Sulphur,  powdered  ;  copper,  thin  foil  or  #30  wire  ;  iron  fil- 
ings, clean  and  fine  enough  to  pass  through  a  sieve  having  60  meshes 
to  the  inch  ;  hydrochloric  acid,  1  to  4  ;  zinc  dust. 

(a)  Fill  the  curved  portion  of  a  test  tube  with  sulphur  and 
heat  it  to  boiling.     Insert  a  strip  of  thin  sheet  copper  (or  fine 
copper  wire)  into  the  boiling  sulphur. 
Result? 

Withdraw  the  strip  and  compare  its  color,  luster,  and  flex- 
ibility with  the  color,  luster,  and  flexibility  of  copper. 
Result?    M^ 


What  is  the  name  of  the  compound  formed  by  the  combination  of 
copper  with  sulphur  ? 

Write  the  equation  representing  the  formation  of  this  compound. 

(6)  Mix  thoroughly  one  part  by  volume  of  finely  powdered 
sulphur  with  two  parts  of  fine  iron  filings.      Put  the  mixture 
into  a  test  tube  and  heat  the  lower  end  of  the  tube  just  sufficiently 
to   color   the   flame   yellow.     When  the  contents  of  the  tube 
commence  to  glow,  withdraw  the  flame. 
Does  the  chemical  action  continue  % 
Why  do  you  think  so  ?     &  1 

Break  the  tube  and  examine  its  contents. 
How  does  it  differ  from  sulphur  in  appearance  ? 


PREPARATION  OF  METALLIC  SULPHIDES  93 

What  gas  is  produced  when  hydrochloric  acid  reacts  with  iron  ? 


Add  one  drop  of  hydrochloric  acid  to  the  substance  taken 
from  the  broken  test  tube;     Cautiously  smell  of  the  gas. 

What  evidence  is  there  that  the  substance  taken  from  the  tube  is  not 
iron  ? 


Write  the  equation  for  thf  reaction. 

* 


(c)  This  should  be  performed  by  the  teacher.  Mix  thoroughly 
a  pinch  of  sulphur  with  an  equal  bulk  of  powdered  zinc. 
Placing  the  mixture  in  a  conical  pile  on  asbestos,  and  holding 
the  burner  at  arms  length,  cautiously  ignite  the  pile  from 
above. 

Result?     £.:.' 

Tf 

Write  an  equation  for  this  reaction. 

•hA  +  llLtt^r  ti  >$' 

Compare  the  action  of  copper  and  zinc  with  sulphur  with  the 
action  of  these  metals  with  oxygen. 


94  LABORATORY  EXERCISES 

£*    3S 
EXPERIMENT   36 

Preparation  and  Properties  of  Hydrogen  Sulphide 

APPARATUS,     Five  test  tubes ;  stopper  and  delivery  tube  to  fit  one  of 

the  test  tubes ;  bunsen  burner. 
MATERIAL.     Iron  sulphide  ;  dilute  hydrochloric  acid  ;  solutions  of  lead 

nitrate,  cadmium  nitrate,  and  hydrogen  peroxide ;  litmus  paper. 

(a)  In  a  test  tube  provided  with  a  stopper  and  a  delivery 
tube  place  two  or  three  small  pieces  of  iron  sulphide  and  cover 
with  dilute  hydrochloric  acid. 

Complete  the  equation : 

FeS  +  £  HC1— >-      ^        + 


Collect  the  gas  by  downward  displacement  in  a  dry  test  tube, 
remove  the  delivery  tube,  and  light  the  gas  in  this  test  tube. 

What  two  products  are  formed  when  the  gas  burns  in  this  way? 
(Examine  the  tube  carefully  for  traces  of  moisture  before  it  becomes 
heated  by  thejlame  of  the  burning  gas.) 

v  //'-,   0    •*+•        S     •  , /;, 

^ '  •  ,':     /^t  6 '  v  '-•  '  „•„ 

How  do  you  identify  them  ?  / 

2^,S  -f  &£^~? 3,'ji . 

What  does  this  show  concerning  the  composition  of  the  gas  ? 

(5)  If  the  gas  in  the  test  tube  burned  quietly,  light  the  gas 
at  the  end  of  the  delivery  tube.  Cautiously  smell  the  gas 
around  the  flame.  A/ • 

Are  all  the  products  formed  the  same  as  before  ? 

State  the  reason  for  your  answer. 


PROPERTIES  OF  HYDROGEN  SULPHIDE  95 

(c)  Place  the  end  of  the  delivery  tube  in  a  test  tube  half 
filled  with  water  and  let  the  gas  bubble  through  the  water  two 
or  three  minutes. 


How  does  the  solution  taste  ? 
What  effect  has  it  on  litmus  ? 


Using  a  small  portion  of  the  solution  of  hydrogen  sulphide  in 
each  case,  add  a  few  drops  of  : 

(1)  a  solution  of  lead  nitrate  ; 

(2)  a  solution  of  cadmium  nitrate.      -0^0 


Results? 

/&**/— 


Complete  tlie 

H2S  +  Pb(N03)2—  *-  _  + 


H2S 


The    cadmium   compound   precipitated  is  used-  as  an  artist's 
pigment. 

It  is  known  as  cadmium    s3-i  i 


Allow  the  gas  from  the  generator  to  bubble  through  a 
solution  of  hydrogen  peroxide  until  a  decided  effect  is  obtained. 
Results  ? 

Complete  the  equation  : 

H2S  +  H202—  *._  1  +  __  g- 


96 


LABORATORY  EXERCISES 


EXPERIMENT   37 

Sulphur  Dioxide 

APPARATUS.  Flask,  250  cc.  with  two-hole  stopper  to  fit ;  thistle  tube  ; 
bent  tube  with  short  arms  ;  bent  tube  with  one  long  arm  ;  rubber  con- 
nection tube  ;  bottle,  150  cc.  ;  two  test  tubes.;  cover  glass;  glass  stir- 
ring rod  ;  ring-stand  with  one  ring  and  one  clamp  ;  bunsen  burner. 

MATERIAL.  Sodium  bisulphite  ;  sulphuric  acid,  1  to  1  ;  pink  carnation  ; 
blue  litmus  paper ;  barium  chloride  solution,  1  to  20 ;  hydrochloric 
acid,  1  to  4  ;  dilute  solution  of  potassium  permanganate,  three  or  four 
small  crystals  dissolved  in  a  liter  of  water. 


i 


(a)  Preparation. 

Arrange  the  apparatus  as  shown  in  Figure 
29.  Be  sure  that  the  end  of  the  thistle  tube 
is  very  near  the  bottom  of  the  flask. 

Pour  10  grams  of  sodium  bisulphite 
(NaHSO3)  into  the  flask,  then  replace  the 
stopper  and  pour  through  the  thistle  tube 
sufficient  water  to  very  little  more  than 
cover  the  end  of  the  tube.  Now  add  sul- 
phuric acid  (1  to  1),  a  little  at  a  time,  until 
chemical  action  starts.  Other  portions  of 
acid  are  to  be  added  from  time  to  time  to 
Figure  29.  cause  the  reaction  to  continue.  Warm  the 

flask  gently,  if  necessary,  to  increase  the  speed  of  the  reaction. 
Complete  the  equation  : 

NaHS03  +  H2S04  — »-  Na2SO4 

(5)  Physical  properties. 

Watch  the  size  of  the  bubbles  of  gas  as  they  rise  through  the 
water  in  a  test  tube  full  of  cold  water,  into  which  the  delivery 
tube  has  been  inserted,  especially  after  the  air  in  the  flask  has 
been  displaced. 

Is  sulphur  dioxide  soluble  in  water? 


SULPHUR  DIOXIDE  97 

Set  the  test  tube'  and  contents  aside  for  future  use,  and 
replace  the  test  tube  with  the  wide  mouth  bottle  (Figure  29). 

Is  sulphur  dioxide  heavier  or  lighter  than  air  ?       •* 
Why  do  you  think  so  f 

Compare  the  odor  of   the  gas  with  the  odor  you  observed 
when  you  burned  sulphur  in  oxygen,  or  in  air. 
Result  ?  $J 

(c)   Chemical  properties. 

Wet  a  pink  carnation  and   put  it  in  a  bottle  of  sulphur 
dioxide.    Cover  the  bottle  and  allow  it  to  stand  for  a  short  time. 
Result  ? 

Touch  a  piece  of  blue  litmus  paper  with  the  end  of  a  stirring 
rod  wet  with  the  liquid  left  in  the  test  tube. 
Result  ? 

Why  is  sulphur  dioxide  not  an  acid  f 

An  oxide  that  unites  with  water  to  form  an  acid  is  an 
acid  anhydride. 

Is  sulphur  dioxide  such  a  compound  ? 
Complete  the  equation  : 

S02  +  H20  — >•     U 

(df)  Test  for  SOr  -  ions. 

SO4~~  ions  unite  with  Ba++  ions  to  form  barium  sulphate, 
a  white  solid  insoluble  in  water  and  in  dilute  hydrochloric  acid. 
This  fact  is  commonly  employed  in  testing  for  sulphuric  acid  or 
a  soluble  sulphate. 


98  LABORATORY  EXERCISES 

Add  a  drop  or  two  of  sulphuric  acid  to  about  10  cc.  of  water 
in  a  test  tube,  and  then  add  a  few  drops  of  a  solution  of  barium 
chloride. 

Result  t 


Complete  the  equation : 

H2S04  +  BaCl2 


Determine  whether  the  precipitate  is  soluble  in  dilute  hydro- 
chloric acid. 
Result  ? 

(0)   Oxidation  of  sulphurous  acid. 

Add  5  cc.  of  the  water  solution  of  sulphurous  acid  to  an  equal 
volume  of  a  dilute  solution  of  potassium  permanganate,  KMnO4. 
Result  ? 

To  the  solution  obtained  add  barium  chloride  solution  and  a 
little  hydrochloric  acid. 
Result  ? 

Into  ivhat  ions  did  the  potassium  permanganate  convert  the  S03 — 
ions  present  in  the  solution  ? 

What  term  is  applied  to  such  a  process  ? 
Wfiat  element  was  taken  from  the  potassium  permanganate  ? 
Is  sulphurous  acid  a  reducing  or  an  oxidizing  agent  9 
Why? 

<j 

^^ 

Is  potassium  permanganate  a  reducing  or  an  oxidizing  agent  ? 
Why? 


PROPERTIES  OF  SULPHUR  DIOXIDE 


99 


EXPERIMENT   38 
Preparation  and  Properties  of  Sulphur  Dioxide.    Reduction  Method 

APPARATUS.  Ring- stand  with  one  ring  and  one  clamp ;  wire  gauze  with 
asbestos  center ;  bunsen  burner  ;  250  cc.  flask  with  stopper  carry- 
ing a  doubly  bent  delivery  tube  and  a  thistle  tube ;  two  wide-mouth 
bottles,  one  of  which  is  provided  with  a  two-hole  rubber  stopper  to  fit ; 
two  bent  tubes  with  rubber  connection  tube  ;  glass  plate. 

MATERIAL.  Copper  (rivets,  turnings,  or  small  clippings) ;  concentrated 
sulphuric  acid ;  pink  carnation ;  blue  litmus  paper ;  barium  chloride 
solution ;  dilute  hydrochloric  acid  ;  hydrogen  peroxide  solution. 

(a)   Preparation. 

Arrange  the  apparatus  as  shown  in  Figure  30.  The  bottle  A 
is  used  as  a  safety  bottle  to  prevent  water  from  being  forced 
back  into  the  hot  concentrated  sul- 
phuric acid,  in  case  the  pressure  in 
the  flask  decreases  during  the  prepa- 
ration of  the  sulphur  dioxide.  Be 
sure  that  the  delivery  tube  from  the 
flask  does  not  extend  more  than  one 
fourth  the  way  down  the  safety  bottle 
A.  Take  the  flask  and,  holding  it 
in  an  inclined  position,  allow  the 
pieces  of  copper  to  slide  down  the 
neck  of  the  flask,  so  as  not  to  break 
the  flask.  Replace  the  stopper  and 
pour  through  the  thistle  tube  suf- 
ficient concentrated  sulphuric  acid 
to  cover  the  copper, 
water. 


Figure  30. 

Fill  one  half  of  the  second  bottle  with 


Caution  ! !  Hot  concentrated  sulphuric  acid  produces  very  severe  burns  when  it 
comes  in  contact  with  the  skin.  The  utmost  care  should  therefore  be  exercised  to 
avoid  being  burned  in  case  the  flask  breaks.  Keep  the  hand  from  under  the  flask 
and  step  back  in  case  the  flask  cracks. 


100  LABORATORY  EXERCISES 

Heat  the  flask  with  a  small  flame.  In  no  case  let  the  flame 
touch  the  glass.  Stop  heating  the  flask  as  soon  as  a  free  evolu- 
tion of  gas  is  obtained. 

C^)   Physical  properties. 

If  the  odor  of  the  gas  is  not  apparent,  it  may  be  detected  by 
wafting  toward  the  nostrils  with  the  hand  a  little  of  the  gas  as 
it  bubbles  from  the  bottle. 

'1 
What  is  the  name  of  the  gas  ? 

What  gas  is  frequently  liberated  when  an  acid  reacts  with  a  metal  ? 

Since  hot,  concentrated  sulphuric  acid  is  an  oxidizing  agent,  what 
compound  of  this  gas  would  be  likely  to  be  formed  9 

So .  '  n  <K  $ 

The  products  actually  formed  depend  on  the  concentration 
of  the  sulphuric  acid  used,  and  the  temperature  at  which  the 
experiment  is  carried  on. 

Assuming  that  sulphurous  acid,  H2S03,  is  the  reduction  product, 

into  what  compounds  would  it  decompose  at  atmospheric  pressure  9 


Complete  the  equation : 

Cu  +  2  H2SO4  — >-  CuSO4 

Watch  the  size  of  the  bubbles  of  sulphur  dioxide  as  they  rise 
through  the  water  in  the  second  bottle. 
Is  sulphur  dioxide  soluble  in  water  ? 
Explain. 

Is  sulphur  dioxide  heavier  or  lighter  than  air  ? 
Why  do  you  think  so  9 

(<0    Chemical  properties. 

Put  a  wet  pink  carnation  into  the  safety  bottle  containing 
sulphur  dioxide. 
Result  9 


PROPERTIES   OF  SULPHUR  DIOXIDE  101 

Test  the  liquid  in  the  second  bottle  with  blue  litmus  paper. 
Result  ? 

Write  an  equation  to  explain  how  an  add  was  produced. 

S6^~t  &t^6  ->    fiJ-sJi 

Why  is  sulphur  dioxide  an  acid  anhydride  ? 


What  is  the  name  of  the  acid  of  which  it  is  the  anhydride  ? 

-^^  ^^^/ 

Add  a  little  hydrogen  peroxide  to  the  solution  in  the  second 
bottle.     Pour  a  little  barium  chloride  solution  into  the  liquid. 
Result  ? 

Determine  whether  the  product  is  soluble  in  dilute  hydro- 
chloric acid. 
Result  ? 

For  what  ion  have  you  just  tested  ? 

Write  the  equation  for  the  reaction  between  sulphurous  acid  and 
hydrogen  peroxide. 


s     ' 

Is  hydrogen  peroxide  an  oxidizing  or  a  reducing  agent  f 


102  LABORATORY  EXERCISES 

fx     3H 

EXPERIMENT   39 
Properties  of  Sulphuric  Acid 

APPARATUS.     Beaker  ;   two  test  tubes  ;  porcelain  evaporating  dish  ;  flask, 

50  cc.  ;  glass  stirring  rod  ;    ring-  stand  with    ring  and  small  clamp  ; 

gauze  with  asbestos  center  ;  bunsen  burner. 
MATERIAL.      Concentrated   sulphuric  acid  ;    dilute  hydrochloric   acid  ; 

barium  chloride  solution,  1  to  20;  sodium  sulphate  solution,  1  to  20; 

cane  sugar  ;  zinc  strips  ;  fine  copper  wire  or  copper  gauze  ;  wood 

splinter. 

(a)   Action  with  water. 

Caution  !  In  mixing  concentrated  sulphuric  acid  with  water,  the  acid  should  be 
slowly  poured  into  the  water,  with  constant  stirring.  The  reverse  method  produces  a 
dangerously  explosive  spattering. 

Pour  a  test-tubeful  of  water  into  a  beaker.  Into  this  water 
slowly  pour  one  sixth  of  a  test-tubeful  of  concentrated  sulphuric 
acitf,  .frequently1  stirring  the  mixture  with  a  glass  rod.  Feel 
the  pu.tS'ide-  jof  .the  ^aker.. 

noticeable  'effect  Is  produced  ? 


Keep  for  parts  (6)  and.(cT)  the  dilute   sulphuric  acid  just 
prepared. 

(£)   Action  with  metals. 

Put  a  zinc  strip  into  one  sixth  of  a  test  tube  of  concentrated 
sulphuric  acid. 

Is  there  much  action  between  the  zinc  and  the  concentrated  sulphuric 


Ponr  the  contents  of  the  test  tube  into  the  sink  and  wash 

down  the  acid  with  water.     Rinse  off  the  zinc  strip  and  return 

it  to  the  test  tube.     Then  pour  upon  it  some  of  the  dilute 

t       sulphuric  ticid  made  in  part  (a). 


Describe  the  action. 


PROPERTIES   OF  SULPHURIC  ACID 


103 


Name  the  gaseous  product,  mid  write  the  equation  for  the  reaction 

•+         —  x^  -> —  —» 


I 


^y     -t 

How  does  dilute  sulphuric  acid  differ 
from  the  concentrated  acid  in  its  action 
u:ith  metals  9 

/ 


Place  some  copper  wire  gauze  or  a 
small  loosely  rolled  ball  of  tine  copper 
wire  in  a  small  flask,  and  add  a  fifth 
of  a  test  tube  of  concentrated  sul- 
phuric acid.  Support  the  flask  on  an 
asbestos  gauze  on  a  ring-stand  in  a 
hood,  and  loosely  clamp  the  neck  of 
the  flask  (Figure  31).  Heat  the  flask 
carefully  with  a  small  flame  until  action 
commences.  Then  remove  the  flame. 


Figure  31 


Describe  the  action. 


Cautiously  smell  the  gaseous  product. 

What  is  it  f  &>r^ 

Wiat  gas  is  usually  liberated  ivhen  an  acid  reacts  ivith  a  metal  f 

Remembering   that   hot,   concentrated  sulphuric   acid   acts  as  an 
oxidizing  agent,  explain  why  we  do  not  get  this  gas  here. 


Fro,,,  which  ofthr  nr!<iin«l 

M-; 

Name  the  salt  formed. 


(  ju 


is  the  sulphur  dioxide  derived  f 


I 


104  LABORATORY  EXERCISES 

Complete  the  equation : 
Cu  + 2H2S04— >-__  _  +  _ 


Mercury  and  silver  react  similarly  to  copper  with  hot  con- 
centrated sulphuric  acid. 

Write  the  equation  for  the  reaction  in  the  case  of  silver. 

(<?)   Dehydrating  action. 

Pour  one  sixth  of  a  test  tube  of  sulphuric  acid  into  an 
evaporating  dish.  Add  a  little  more  than  enough  cane  sugar 
to  soak  up  the  acid.  Allow  the  action  to  continue  until  a  de- 
cided result  is  obtained. 

/  .f    • 

Describe  the  action  that  occurs. 

Which  element  of  the  cane  sugar  molecules  (C^H^On)  gives  the 
color  to  the  residue  in  the  dish,  ?      0 


What  elements  did  the  concentrated  sulphuric  acid  remove  from 
the  cane  sugar  molecules  f 

Dip  a  wooden  splinter  into  concentrated  sulphuric  acid. 
Results? 

Explain  the  effect  of  the  acid  upon  the  wood,  which  is  mainly 
cellulose,  a  substance  represented  by  the  formula  C6H1005. 

£4     /•:-  'V-      £        6/> 

Complete  the  statement  : 

When  sulphuric  acid  acts  as  a  dehydrating  agent  on  com- 
pounds,   it    removes   from    them     /</y.y-:.  .".-?/,.    and  _     //•  /  -•. 
...-?./'.      . 
Why  is  sulphuric  acid  used  in  drying  gases? 

"      -c 


as 


Test  for  a  sulphate. 
To  a  little  sodium  sulphate  solution  in  a  test  tube,  add  a  few 
cubic  centimeters  of  barium  chloride  solution. 


PROPERTIES  OF  SULPHURIC  ACID  105 

Describe  the  color  and  character  of  the  compound  produced. 


Write  the  equation  for  its  formation. 

->  M  ?- 

Add  dilute  hydrochloric  acid   to  the   precipitated    barium 
sulphate. 
Result? 

Using  barium  chloride  solution  and  dilute  hydrochloric  acid, 
repeat  the  test  with  dilute  sulphuric  acid,'ftydrogen  sulphate. 
Result?         .       .         '4L 

State  the  test  for  a  sulphate. 

toJb  bss-  trt<**$-%t^ 

DRAWING,  PART  (&) 


< 


106 


LABORATORY  EXERCISES 


EXPERIMENT   40 

Preparation  of  Nitrogen 

APPARATUS.     Pneumatic  trough  ;  phosphorus  stand  (Figure  32)  consist- 

ing of  (a)  cork  to  fit  hole  in  shelf  of  trough  ;  (ft)  #  16  copper  wire; 

and    (c)    blackboard    crayon  ;    iron   forceps  ;    stirring   rod  ;    burner  ; 

wide-mouth  bottle,  8  oz.  ;    glass  plate. 
MATERIAL.     Small  piece  of  phosphorus  kept  under  water  ;  filter  paper  ; 

wooden  splinter. 

Hollow  a  cavity  in  the  end  of  a  piece  of  blackboard  crayon. 
Place  it  on  the  wire  stand.  (J,  Figure  32)  and  insert  cork  in  the 
hole  in  the  shelf  of  a  pneumatic  trough.  Fill  the  trough  with 
water  to  1  cm.  above  the  shelf.  Have  close  at  hand  an  8  oz. 
wide-mouth  bottle. 

Caution  !  Yellow  phosphorus  should  never  be  handled  except 
under  water. 

With  a  pair  of  forceps,  take  a  piece  of  phos- 
phorus about  half  the  size  of  a  pea,  remove  the 
adhering  water  with  a  bit  of  filter  paper,  and 
place  the  phosphorus  in  the  hollow  of  the  crayon. 

Touch  the  phosphorus  with  a  warm  stirring  rod 
and  immediately  invert  over  it  the  wide-mouth 
bottle,  and  let  it  rest  on  the  shelf  of  the  trough. 
Carefully  note  and  record  the  results. 


Figure  32. 

o,  cork  ;  b,  #  1 6 
copper    wire ; 

When  the  white  cloud  in  the  bottle  has  cleared, 
press  the  phosphorus  stand  from  below  up  into  the  bottle. 
Slide  the  bottle  to  the  edge  of  the  shelf  and  allow  the  phos- 
phorus stand  to  drop  down  into  the  trough. 

Cover  the  mouth  of  the  bottle  with  a  glass  plate,  invert  it, 
and  set  it  on  the  desk.  A. 


PREPARATION   OF  NITROGEN 

Describe  the  appearance  of  the  nitrogen. 

a  lighted  splinter  into  the  bottle. 


107 


Result?    \g)j^£^ 

What  constituent  of  the  air  was  removed  by  the  phosphorus? 

WJiat  other  constituents  still  remain  with  the  nitrogen  ? 
&$Jt~  sfLsO^JL  -*£'£'t£'£x^    to  0(s£&^*    - 

Dispose  of  the  phosphorus  stand  as  directed  by  the  instructor. 

Alternative  Method 

APPARATUS.  Pneumatic  trough ;  two  wide-mouth  bottles;  glass  plate; 
ring-stand  with  one  ring  and  one  clamp ;  250  cc.  Erlenmeyer  flask 
with  two-hole  rubber  stopper  to  fit ;  thistle  tube ;  delivery  tube ;  wire 
gauze  with  asbestos  center ;  bunsen  burner ;  test  tube. 

MATERIAL.  Sodium  nitrite, 
NaN02;  ammonium  chloride; 
wooden  splinter. 

Put  15  grams  of  sodium 
nitrite  and  10  grains  of  am- 
monium chloride  into  a  250  cc. 
Erlenmeyer  flask. 

Fit  the  flask  with  a  two- 
hole  rubber  stopper  carrying 
a  thistle  tube  and  a  delivery 
tube  leading  to  a  pneumatic 
trough.  Support  the  flask 
on  a  wire  gauze  resting  on 
the  large  ring  of  a  ring-stand 
(Figure  33). 

Add  a  test-tubeful  of 
tube. 


Figure  33. 

the  *lask  through  the  thistle 
these  two  as  ^ 


108  LABORATORY  EXERCISES 

Caution !  !    Avoid  overheating  the  flask,  so  as  to  prevent  an  explosive  de- 
composition. 

Gently  heat  the  flask  so  that  the  nitrogen  will  be  evolved  at 
a  temperature  considerably  below  the  boiling  point  of  water. 
In  case  frothing  occurs  from  overheating,  pour  a  few  cubic 
centimeters  of  cold  water  into  the  thistle  tube. 

After  the  air  has  been  displaced  from  the  flask,  collect  the 
nitrogen  in  wide-mouth  bottles. 

Lower  a  lighted  splinter  into  a  bottle  of  nitrogen. 
Result  ? 

<.// 
Has  the  nitrogen  of  the  air  an  odor  9 

Smell  a  bottle  of  the  nitrogen  collected. 

What  does  this  result  show  about  the  nitrogen  collected  f 


The  nitrogen  in  the  present  experiment  results  from  the 
decomposition  of  ammonium  nitrite.  This  compound  is  so 
unstable  that  it  is  freshly  prepared  by  the  interaction  of 
ammonium  chloride  and  sodium  nitrite. 

Complete  the  equations : 

NH4C1  +  NaN02  — >-  NH4NO2  +  _ 

NH4NO2— ^ +' 


DRAWING 


PREPARATION  AND  PROPERTIES  OF  AMMONIA        109 

EXPERIMENT  41 
Preparation  and  Properties  of  Ammonia 

APPARATUS.  Ring-stand;  clamp;  test  tube  rack;  three  test  tubes, 
one  fitted  with  one-hole  stopper  and  delivery  tube ;  perforated  card- 
board square ;  bunsen  burner ;  enameled  pan. 

MATERIAL.  Slaked  lime;  ammonium  chloride;  ammonium  sulphate; 
sodium  hydroxide  solution ;  red  and  blue  litmus  paper. 

(a)   Preparation  of  ammonia. 

Take  a  little  ammonium  chloride  in  one  hand  and  in  the  other 
a  little  slaked  lime  (dry).  Smell  of  each.  Rub  the  two  to- 
gether between  the  palms  of  the  hands.  Smell  the  mixture 
cautiously.  Bring  a  moist  strip  of  litmus  paper  near  t 
mixture. 

Results?    #UA*U    ft 

' 


(£>)  Repeat,  using  ammonium  sulphate  and  slaked  lime.     As 
before,  smell,  and  apply  litmus  test. 
Results? 


(c)  To  a  little  sodium  hydroxide  solution  in  a  test  tube  add 
a  small  amount  of   ammonium    chloride.     Heat  gently,  smell 
cautiously,  and  test  with  litmus  as  before. 
Results  ? 


Ammonium    chloride,    NH4C1,    and    ammonium    sulphate, 
(NH4)2SO4,  are  salts. 

Regarding  the  reaction  between  sodium  hydroxide  and  ammonium 
chloride  as  a  double  replacement,  name  the  two  products  formed. 
.    ttydsurj^tl  ^WeU^n^   wUk^' 

Write  the  equation  showing  these  two  as  products. 

i  .^& 


110 


LABORATORY  EXERCISES 


Ammonia  gas,  NH3,  results  from  the  decomposition  of  one  of 
the  products. 

Write  the  equation  for  this  decomposition. 

Complete  the  equation  for  the  action  in  part  (a). 
Ca(OH)2+2NH4Cl  — ^_         _  + 


Write  a  single  equation  for  the  action  in  part  (b). 


How  could  you  prove  that  a  substance  given  you  ivas  an  ammonium 
salt  ? 

1  TL         /,-  **./JAAA-i  /'*,?•< 

\    2^4    ••-^/&  Mjt       '.ifrWw  -nr,l< 


(c?)  On  a  piece  of  paper,  mix  a  quarter  of 
a  test-tubeful  of  ammonium  chloride  with  a 
quarter  of  a  test-tubeful  of  slaked  lime.  Put 
the  mixture  into  a  test  tube  provided  with  a 
delivery  tube  for  the  collection  of  the  gas  by 
upward  displacement  (see  Figure  34).  Warm 
the  mixture  very  gently.  Fill  a.  dry  test  tube 
with  the  gas. 


Figure  34. 


)   Properties  of  ammonia. 

What  is  the  color  of  the  ammonia  gas  ? 


'l 


Is  this  gas  lighter  or  heavier,  than  air  9 


(/)  Place  a  test  tube  of  ammonia  mouth  downward  in  a  dish 
of  water. 
Result? 

What  does  this  show  9 

ft 
v 


'  AMMONIUM  COMPOUNDS  111 

EXPERIMENT  42 
.* 

Ammonium  Compounds 

APPARATUS.  Test  tube  with  stopper  and  single-bend  delivery  tube; 
four  other  test  tubes  ;  ring-stand  with  one  clamp  ;  bunsen  burner. 

MATERIAL.  Ammonium  chloride ;  slaked  lime ;  concentrated  hydro- 
chloric acid  ;  concentrated  sulphuric  acid  ;  sodium  hydroxide  solution, 
1-10  ;  red  litmus  paper  ;  blue  litmus  paper  ;  labels. 

On  a  piece  of  paper,  mix  thoroughly  5  grams  of  ammonium 
chloride  and  10  grams  of  dry,  slaked  lime.     Notice  the  char- 
acteristic odor  of  ammonia.     Place  the  mix- 
ture  in   a  dry  test  tube,  provided   with   a 
stopper    and    delivery   tube.       Clamp   it  in 
a  nearly  horizontal  position  with  the  delivery 
tube  pointing  down  (Figure  35).     Have  at 
hand  three  test  tubes  :   (a)  a  dry  test  tube  to 
which  2  drops  of  concentrated  hydrochloric 
acid  have  been  added ;    (6)  a  test  tube  con- 


taining 1  drop  of  sulphuric  acid ;   (<?)  a  test  Figure  35 

tube  containing  water  to  the  depth  of  1  inch. 

(a)  Warm  gently  the  test  tube  containing  the  mixture,  and 
bring  the  delivery  tube  into  the  test  tube  containing  the  drops 
of  hydrochloric  acid,  until  a  solid  is  formed.  This  solid  is 
ammonium  chloride,  NH4C1. 

Write  the  equation  for  the  reaction. 

Was  there  any  heat  developed  when  it  formed  ? 

Label  and  reserve  the  material. 

(6)  Similarly  use  the  test  tube  containing  the  single  drop  of 
sulphuric  acid.  The  solid  formed  in  this  case  is  ammonium 
sulphate,  (NH4)2SO4. 

Write  the  equation  for  the  reaction. 


112  LABORATORY  EXERCISES' 

Was  there  any  heat  developed  when  it  formed  f 

Label  and  reserve  the  material. 

(0)  In  like  manner,  bring  the  delivery  tube  into  the  test 
tube  containing  water,  but  be  particularly  careful  that  the  de- 
livery tube  does  not  touch  the  water.  Observe  the  top  of  the 
water. 

Is  there  any  sign  of  action  ? 

Is  there  any  heat  developed  ? 

Test  the  liquid  with  litmus. 
Result  ? 
Has  the  liquid  any  odor  ? 

The  liquid  is  a  solution  of  ammonium  hydroxide,  NH4OH,  an 
unstable  base  which  is  commonly  used. 
Write  the  equation  for  its  formation. 

(c?)  Using  half  of  this  solution  of  ammonium  hydroxide, 
boil  the  liquid  for  three  minutes,  while  holding  a  piece  of 
moistened  litmus  paper  across,  but  not  touching,  the  mouth  of 
the  test  tube. 

What  indication  is   there  that  something  besides  ivater  vapor  is 

escaping  ? 

Label  and  reserve  the  material.  Ammonium  hydroxide  is 
very  unstable.  It  decomposes,  forming  water  and  gaseous 
ammonia  (NH3). 

Complete  the  equation  : 

NH4OH— ^ + ._ 


(e)  Using  the  other  part  of  the  ammonium  hydroxide  solu- 
tion obtained  in  part  (<?),  add  to  it  two  drops  of  hydrochloric 
acid,  mix  well,  and  if  there  is  any  odor,  warm  the  solution 


AMMONIUM  COMPOUNDS  113 

gently  until  the  odor  has  disappeared.     Label  and  reserve  this 
solution  for  part  (A). 
Write  the  equation. 

(/)   Using   the   test   tube  containing   the  solid  ammonium 
chloride  (part  a),  warm  it  gently  at  the  spot  where  the  most 
solid  seems  to  be. 
Result  ? 

Would  this  have  happened  to  sodium  chloride  9 

When  the  test  tube  has  cooled,  add  a  little  water. 
Does  the  ammonium  chloride  dissolve  9 

How  does  it  react  with  red  and  with  blue  litmus  9 


Label  and  reserve  the  material  for  part 
(</)  Add  a  little  water  to  the  test  tube  containing  the  solid 
ammonium  sulphate. 

Does  it  dissolve  in  water  9 

How  does  it  react  with  litmus  9 

Label  and  reserve  the  material  for  part  (A). 

Ammonium  compounds  resemble  chemically  the  compounds 
of  potassium  and  of  sodium.  In  the  ammonium  compounds, 
the  group  of  atoms  (NH^  acts  like  an  atom  of  sodium  or 
potassium. 

In    this    experiment,   in    what    two    cases    has    the    ammonium 

hydroxide  acted  in  the  same  manner  as  sodium  hydroxide  would  have 

done  ? 

In  which  case  did  it  act  differently  9 


114 


LABORATORY  EXERCISES 


(Ji)   Test  for  ammonium  compounds. 

To  detect  ammonium  compounds,  convert  the  compound  into 
the  hydroxide  and  identify  the  unstable  ammonium  hydroxide 
by  the  ammonia  gas  resulting  from  its  decomposition. 


To  each  of  the  four  materials  reserved,  after  noticing  whether 
there  is  any  odor,  add  5  or  6  drops  of  sodium  hydroxide  solution. 
Notice  whether  there  is  an  odor,  and,  while  holding  a  piece  of 
moistened  litmus  paper  just  above  the  mouth  of  the  test  tube, 
warm  the  tube  gently.  Observe  carefully  the  result  in  each 
case. 

Tabulate  results  as  indicated  below. 

TABLE 


MATERIAL  IN  TEST 
TUBE  FROM 

ODOR  BEFORE 
ADDING  NaOH 

ODOR  AFTER 
ADDING  NaOH 

ACTION  WITH 
LITMUS 

d 

e 
f 

9 

Complete  the  equations: 
NH4Cl+NaOH     — *- 
(NH4)2S04  +  NaOH     — >- 
NH4OH  heated      -+ 
NH4C1  +  Ca(OH)2      — >- 

Having  performed  the  test  for  ammonia  on  these  four  samples,  how 
could  you  now  tell  whether  the  original  material  was  a  chloride  or  a 
sulphate  ? 


PREPARATION  AND   PROPERTIES   OF  NITRIC  ACID     115 


EXPERIMENT  43 

Preparation  and  Properties  of  Nitric  Acid 

APPARATUS.     Retort,  100  cc.  ;   two  test  tubes  ;   battery  jar;  ring-stand 

with  large  ring  ;   wire  gauze  with  asbestos  center  ;    clamp  ;  bunsen 

burner  ;  funnel  or  thistle  tube  ;  flask. 
MATERIAL.    Sodium  nitrate  ;  concentrated  sulphuric  acid  ;  concentrated 

hydrochloric  acid  ;  ferrous  sulphate  solution,  freshly  prepared;  copper 

strip;  excelsior;  unknowns. 

Caution  !    Concentrated  sulphuric  and  nitric  acids  are  dangerous  to  both  flesh  and 
clothing. 

(tf)   Preparation. 

Put  about  15  grams  of  sodium  nitrate  into  a  tubulated  retort. 
Place  the  retort  on  a  wire  gauze.  Insert  the  neck  of  the  retort 
as  far  as  possible,  but  not 
tightly,  into  a  flask  partly 
immersed  in  water  (Figure 
36). 

Clamp  the  retort  in  position 
and  pour  10  cc.  of  concen- 
trated sulphuric  acid  through 
a  funnel,  or  thistle  tube,  upon 
the  nitrate. 

Replace  the  stopper  and 
heat  the  contents  of  the  retort 
gently.  Be  careful  not  to 
allow  the  flame  to  pass  through 


the  gauze. 

What   two  changes  of  state 

£ 


Figure  36. 
take  place  in  the  distillation  of  the 


acid? 


Distil,  using  moderate  heat,  as  long  as  any  nitric  acid  runs 
down  the  neck  of  the  retort. 

Allow  the  retort  and  its  contents  to  cool  without  removing  the 
retort  from  the  stand. 


116  LABORATORY  EXERCISES 

Complete  the  equation : 

Why  does  this  reaction  go  to  an  end  f 
A-J      /WPiitt'i  £•(&*> 


Upon  what  characteristic  of  sulphuric  acid  does  its  use  in  this 
experiment  depend  f 

•^  C    i      '-i    •  '.-    /       « 

(6)   Oxidizing  action  of  nitric  acid. 

N.B.   The  acid  collected  is  much  more  active  than  the  ordinary  nitric  acid. 

Use  it  very  carefully  and  throw  all  solid  materials  in  a  waste 
jar  immediately  after  examining  them. 

Put  into  a  test  tube  1  cc.  of  the  acid  that  you  have  pre- 
pared, and  thrust  in  a  small,  loose  plug  of  excelsior  so  that  it 
remains  about  an  inch  above  the  acid.  Hold  the  test  tube  by 
means  of  a  holder  and  heat  the  acid  until  it  boils  vigorously, 
and  the  vapor  reaches  the  excelsior.  After  a  moment,  hold 
the  tube  so  that  the  flame  is  directly  under  the  excelsior  for  a 
few  seconds. 

-*  \          J  /V    / 

Results  ? 

^ •  /#  •  x'l/7  f.t  A  /'( /   ^"/>V  i '»  '  -  v*?  ** 


This  action  is  chiefly  due  to  the  very  strong  oxidizing  char- 
acter of  nitric  acid. 

Fill  the  curved  bottom  of  the  test  tube  (1  cc.)    with   the 
acid   you  have  prepared.       Add  twice  the  volume  of   hydro- 
chloric acid  and  heat  the  mixture. 
What  change  in  color  takes  place  ? 

Smell  cautiously  the  gas  issuing  from  the  test  tube. 
What  is  this  gas  ? 


frt*- 


PREPARATION  AND  PROPERTIES  OF  NITRIC  ACID     117 

Complete  the  equation  :  , 

HNOS+        .3  HC1-W//   fl  +  3'fs..    +NO 


Explain  how  this  shows  the  oxidizing  power  of  nitric  add. 


Such  a  mixture  of  nitric  and  hydrochloric  acids  is  known  as 
aqua  regia. 

((?)   Action  of  nitric  acid  with  metal. 

Put  a  small  strip  of  copper  into  a  test  tube  and  add  a  few 
drops  of  the  acid  that  you  have  prepared  and  a  few  drops  of 
water. 

Result  ? 


Supposing  that  hydrogen  is  at  first  formed,  as  in  the  typical  action 
of  an  acid  with  a  metal,  what  further  action  would  occur  as  a  result 
of  the  property  of  nitric  acid  shown  in  part  (b) 


6  . 

Dissolve  a  very  small  amount  of  sodium  (or  potassium)  nitrate 
in  2  cc.  of  water.  Add  an  equal  volume  of  ferrous  sulphate 
solution.  Hold  the  tube  in  an  inclined  position,  and  pour  slowly 
down  the  side  of  the  tube  2  cc.  of  concentrated  sulphuric  acid. 
The  heavy  acid  will  run  down  the  tube  and  form  a  separate 
layer  under  the  mixture  of  the  other  two  solutions. 


Describe  the  appearance  between  the  two  layers.  £j  £&l& 


This  is  a  very  delicate  indication  of  a  nitrate.  Repeat  the 
test  once  or  twice  using  unknown  solutions  furnished  by  the 
instructor. 

Record  the  results  obtained  with  the  unknown  solutions. 


118  LABORATORY  EXERCISES 

EXPERIMENT   44 
Preparation  and  Properties  of  Nitric  Oxide 

APPARATUS.  Four  wide-mouth  bottles  (6  to  8  oz.)  ;  2-hole  rubber  stopper 
to  fit  wide-mouth  bottle;  thistle  tube;  delivery  tube;  pneumatic 
trough  or  dish;  oxygen  generator,  consisting  of  wide-mouth  bottle 
(6  oz.),  with  a  2-hole  rubber  stopper  carrying  a  delivery  tube  and  a 
funnel  having  a  glass  rod  with  one  end  ground  into  the  funnel  so  as 
to  form  a  stopper  (Figure  37)  ;  test  tube. 

MATERIAL.  Copper  (wire,  rivets,  or  turnings)  ;  concentrated  nitric 
acid;  sodium  peroxide. 

(a)   Preparation. 

Arrange  a  wide-mouth  bottle  with  a  stopper  carrying  a 
thistle  tube  and  delivery  tube.  Place  in  the  bottle  about  10  g. 
of  copper  and  cover  with  a  test-tubeful  of  water. 

Pour  about  one  third  of  a  test-tubeful  of  concentrated  nitric 
acid  through  the  thistle  tube  of  the  generator  and  wait  for  the 
action  to  start.     Collect  the  gas  by  the  displacement  of  water. 
To  maintain  the  action  in  the  generator,  add  from  time  to  time 
small  quantities  of  the  concentrated  nitric  acid. 
.Note  the  color  of  the  gas  that  first  appears  in  the  generator,  /v 
Why  does  it  not  appear  in  the  collecting  bottle  ? 


What  is  the  difference  in  color  between  this  gas  and  the  one  that 


does  collect  in  the  bottle  9 


The  gas  that  collects  in  the  bottle  over  water  is  nitric  oxide, 
NO. 

Collect  one  full  bottle,  and  another  bottle  half  full  of  the  nitric 
oxide,  and  let  them  stand  in  the  trough  for  use  later. 

Note  the  color  of  the  liquid  in  the  generator.     This  color  is 
characteristic  of  the  water  solution  of  cupric  salts. 

What  gas  is  often  produced  by  the  action  of  an  acid  with  a  metal  ? 


PREPARATION  AND  PROPERTIES   OF  NITRIC  OXIDE     119 


What  oxidizing  action  prevents  our  getting  this  gas 
here? 


Name  the  product  that  is  formed  instead. 


\ 


The  removal  of  oxygen  from  certain  nitric  acid 
molecules  results  in  their  reduction  to  nitric  oxide  and  water. 


Complete  the  equation  : 
3  Cu  +  8  HN03  —  >- 


Cu(N03)2  + 


(b)  Action  with  oxygen. 

Obtain  from  the  instructor  one  of  the  bottles  for  generating 
oxygen  (Figure  38)  by  the  action  between  water  and  sodium 

peroxide : 
2  Na2O2  +  2  H2O 

— >-  4  NaOH  +  O2 

Gently  loosen  the  stop- 
per in  the  funnel  so  as 
to  allow  a  few  drops  of 
the  water  in  the  funnel 
to  fall  upon  the  sodium 
peroxide  at  the  bottom 
of  the  generator. 

Allow  the  air  in  the 
delivery  tube  to  be  dis- 
placed by  the  oxygen. 
If  the  action  stops,  let 
another  drop  of  water 
fall  on  the  peroxide. 


Figure  38. 


Caution!    To  avoid  violent  action,  use  water  in  small  amounts  with  intervals 
between. 


120  LABORATORY  EXERCISES 

Pass  oxygen,  a  little  at  a  time,  by  means  of  the  delivery  tube, 
into  the  bottle  that  is  half  full  of  nitric  oxide,  which  is  stand- 
ing in  the  pneumatic  trough. 

What  are  the  two  noticeable  results  ? 


In  what  respect  does  this  colored  gaseous  product  differ  in  compo- 
sition from  the  nitric  oxide? 


Complete  the  equation : 

2  NO  +  Q3  — >-  ^/    / 

(tf)   Action  with  air. 

Allow  the  full  bottle  of  nitric  oxide  to  escape  into  the  air. 
What  evidence  of  a  chemical  change  do  you  observe  ? 

'  ^k-4*  5-  <V       &  -'  ^  '*#  !•  •"*- ' "  <•       ^"P    &    *~ 

/ 

With  what  gas  in  the  air  does  the  nitric  oxide  combine? 

Account  for  the  reddish  brown  gas  that  appeared  in  the  generator 
at  the  beginning  of  part  (a).     ^ 


Compare  the  solubility  in  water  of  nitric  oxide  and  of  nitrogen 
peroxide.      |\ 


DRAWING 


PREPARATION  AND  PROPERTIES  OF  NITROUS  OXIDE     121 


EXPERIMENT   45 
Preparation  and  Properties  of  Nitrous  Oxide 

APPARATUS.  Flask  and  small  bottle,  with  stoppers  and  delivery  tubes 
as  shown  (Figure  39)  ;  ring- stand ;  clamp ;  bunsen  burner ;  three 
bottles  (6  oz.)  ;  dish  of  water  ;  glass  plate  ;  test  tube,  fitted  with 
rubber  stopper  carrying  delivery  tube. 

MATERIAL.  Ammonium  nitrate  ;  anhydrous  copper  sulphate  ;  splinter; 
copper  turnings  ;  concentrated  nitric  acid. 

(a)  Put  10  grams  of  pure  crystallized  ammonium  nitrate 
into  the  flask  and.  arrange  the  apparatus  as  shown  in  Figure  39. 
Heat  the  flask  very  cautiously,  keeping  the  flame  in  constant 
motion.  If  brown  fumes 
appear  in  the  flask  during 
the  heating,  allow  the  flask 
to  cool  a  little. 


Figure  39. 


Caution !  The  brown  fumes  indi- 
cate a  decomposition  that  may  be- 
come explosively  violent. 

Collect  one  bottle   and 
two  half  bottles  of  nitrous 
oxide  by  the  displacement 
of  water.     Leave  the  half-filled  bottles  standing  in  water  until 
needed  for  parts  (6)  and  (d). 

Drop  a  little  anhydrous  copper  sulphate  into  the  small  bottle. 
What  liquid  is  in  the  bottle  ? 

Complete  the  equation : 

NH4NO3  - 

Has  the  gas  an  odor? 

(6)  Place  the  palm  of  the  hand  over  the  mouth  of  the  half- 
filled  bottle.     Press  down  tightly  and  shake  vigorously. 
to**™    ^M4£,- 


122  LABORATOEY  EXERCISES 

Explain. 

(<?)  Lower  a  glowing  splinter  into  a  bottle  of  nitrous  oxide. 
Result? 


Place  small  pieces  of  copper  turnings  in  a  test  tube  pro- 
vided with  stopper  and  delivery  tube.  Cover  the  copper  with 
nitric  acid,  immediately  insert  the  stopper,  and  place  the  end 
of  the  delivery  tube  under  the  water  of  the  dish.  As  soon  as 
colored  gas  no  longer  shows  in  the  test  tube  generator,  insert 
the  end  of  the  delivery  tube  under  the  mouth  of  one  of  the 
bottles  that  was  half  filled  with  nitrous  oxide. 

Does  nitrous  oxide  react  with  nitric  oxide  in  the  same  way  that 
oxygen  did  in  Experiment  44% 

How  could  you  determine  ivhether  a  gas  was  nitrous   oxide  or 
oxygen ? 


DRAWING 


PREPARATION  AND  PROPERTIES   OF  BROMINE       123 


EXPERIMENT  46 
Preparation  and  Properties  of  Bromine 

APPARATUS.  Ring- stand  ;  clamp  ;  four  test  tubes  ;  one-hole  stopper 
and  a  delivery  tube  ;  beaker ;  bunsen  burner ;  test  tube  rack. 

MATERIAL.  Potassium  bromide  ;  manganese  dioxide  ;  sulphuric  acid, 
2  to  1 ;  carbon  disulphide  ;  chlorine  water. 

Caution !    Keep  flames  away  from  carbon  disulphide.    Its  vapor  is  explosive  when 
mixed  with  air. 


(a)   Preparation. 

On  a  piece  of  paper,  mix 
1  gram  of  potassium  bromide 
with  an  equal  bulk  of  man- 
ganese dioxide. 

Fit  a  test  tube  with  a  one- 
hole  stopper  carrying  a  delivery 
tube.  Pour  about  3  cc.  of  sul- 
phuric acid  (2  to  1)  into  the 
test  tube,  and  add  the  mixture 
of  potassium  bromide  and  man- 
ganese dioxide.  Clamp  the 
tube  containing  the  mixture  so 


Figure  40. 


that  the  delivery  tube  shall  extend  to  the  bottom  of  an  empty 
test  tube,  standing  in  a  beaker  of  water  (Figure  40).  Warm 
the  test  tube  containing  the  mixture  very  gently. 

What  is  the  color  of  the  bromine  vapor  and  of  the  liquid  bromine? 

'^.^74^7^' 

Nearly  fill  the  test  tube  containing  the  bromine  with  water. 
Save  the  mixture  for  future  use. 

Is  bromine  heavier  or  lighter  than  water  ?     l+CfrV~T- 

State  reason  for  your  answer. 

Jfcti-  Jfaf*  &' 

What  compounds  would  we  expect  to  have  formed  by  the  action  of 
potassium  bromide  with  sulphuric  acid  ? 


/ 


124  LABORATORY  EXERCISES 

Complete  the  following  equations,   and  draw   lines   through  the 
products  that  do  not  remain  as  permanent  products  of  the  reaction : 

2  KBr  +  HoSOj— ^  AV  .^  £r^7&   . 
MnO2  +  H2SO4  — >-  MnSO4+  ft-       _  +  _ 

Show  by  an  equation  how  the  two  temporary  products  that  you 
have  crossed  out  react  with  each  other : 

£//&»  +6  ->  .  tt±b  +  ^i 

Show  the  Jinal  products  of  the  reaction  by  completing  the  following 
equation : 

KBr  +  Mn02+  H2SO4  — >- 

lA^MxC      '  y 

(6)   Solubility  of  bromine. 

Add  a  few  drops  of  carbon  disulphide  to  a  test  tube  one  third 
full  of  water,  and  shake  the  contents. 

Are  the  two  liquids  miscible:  that  is,  are  they  completely  soluble  in 
each  other  ?     J{# 

To  what  extent  is  bromine  soluble  in  water  9 

(<?)  Add  a  few  drops  of  the  bromine  water  obtained  in  part 
(a)  to  the  mixture  of  carbon  disulphide  and  water.  Shake  the 
resulting  mixture  vigorously  and  then  allow  it  to  stand  for  a 
short  time. 

What  color  does  the  bromine  impart  to  the  carbon  disulphide  ? 

/?/  C{  dA.<~4*r  — 

Does  all  of  the  bromine  dissolve  in  the  carbon  disulphide  ? 

pe.o  • 

Is  bromine  more  soluble  in  water  or  in  carbon  disulphide  ? 

(c?)   Test  for  a  bromide. 

Dissolve  a  small  crystal  of  potassium  bromide  in  2  or  3  cc. 
of  water,  add  a  little  carbon  disulphide,  and  shake  the  mixture. 
Save  the  resulting  mixture  for  part  (e). 


PREPARATION  AND  PROPERTIES   OF  BROMINE        125 

Does  bromine,  when  combined  with  other  elements,  color  carbon  di- 
sulphide 


In  what  state  must  the  bromine  be  to  give  the  test  with  carbon 
disulphide  ?   '  X^    Urw*L^ 

(0)  To  the  solution  obtained  in  part  (d)  add  a  few  drops  of 
chlorine  water  and  shake  the  mixture. 

What  evidence  is  there  that  bromine  has  been  set  free  by  action  of 
the  chlorine  f 


Complete  the  equation  : 

ZKBr  +  Cl2  — 
What  name  is  given  to  this  type  of  chemical  reaction 


Which  has  the  greater  heat  of  formation,  potassium  bromide  or 
potassium  chloride  (see  Experiment  27)  ? 


Give  a  test  for  a  bromide. 


DRAWING 


126  LABORATORY  EXERCISES 

i*  3? 

EXPERIMENT   47 
Preparation  and  Properties  of  Iodine 

APPARATUS.  7  test  tubes  ;  test  tube  rack  ;  bunsen  burner  ;  paper, 
15  x  5  cm. 

MATERIAL.  Potassium  iodide  ;  manganese  dioxide  ;  sulphuric  acid, 
2  to  1  ;  alcohol  ;  potassium  iodide  solution  ;  chloroform  or  carbon 
disulphide  ;  chlorine  water  ;  bromine  water  ;  wooden  splinters. 

(#)  Preparation. 

/I 
Mix  on  a  piece  of  paper  1  gram  of  potassium  iodide  with 

one-fourth  its  bulk  of  manganese  dioxide.  Roll  the  paper  into 
a  cylinder  and  insert  it  with  its  contents  into  a  dry  test  tube  held 
horizontally.  Raise  the  tube  to  a  vertical  position,  so  that  the 
mixture  will  fall  to  the  bottom  without  touching  the  sides. 
Withdraw  the  paper,  and  add  2  cc.  of  sulphuric  acid  (2  to  1). 
Warm  the  contents  of  the  tube  very  gently. 
Results  9  { 


Describe  the  deposit  of  iodine. 


/    '       «/  ' 


Complete  the  following  equations,  drawing  lines  through  the  for- 
mulas of  substances  that  do  not  remain  as  permanent  products  of  the 
reaction. 

1.KI+          H2SO4  — 
MnO2  +          H2SO4—  • 


Write  another  equation  to  show  how  the  tivo  subst 
have  crossed  out  react  with  each  other. 

}..  V-L-t  d   ->  /Mf  /, 

»£••  .  > 

Show  the  Jinal  products  of  the  reaction  by  completing  the  following 
equation : 

KI  +  MnOa+    t.H2S04— ^^J  1+4      £.  4r2:      -  +  -" 


PREPARATION  AND  PROPERTIES  OF  IODINE 


127 


(6)   Effect  of  various  solvents  on  iodine'. 

With  a  splinter  remove  small  portions  of  the  solid  that  ad- 
heres to  the  sides  of  the  tube,  and  try  to  dissolve  the  iodine 
in  (1)  water,  (2)  alcohol,  (3)  a  water  solution  of   potassium 
iodide,  (4)  carbon  disulphide  (or  chloroform). 
Record  your  results  in  a  tabular  form: 

TABLE 


SOLVENT 


COLOR  op  SOLUTION 


DEGREE  OP  SOLUBILITY 
(Slightly,  moderately,  or  very) 


(e)   Carbon  disulphide  test  for  iodine. 

Put  3  cc.  of  water  and  a  very  small  crystal  of  iodine  into  a 
test  tube  ;  into  another  test  tube  put  an  equal  volume  of  a 
solution  of  potassium  iodide.  To  each  test  tube,  add  a  few 
drops  of  carbon  disulphide  (or  chloroform).  Shake  each 
mixture  thoroughly. 

In  which  case  does  the  carbon  disulphide  acquire  a  color  ? 

&*  /££*/  /£t^«.  ^o-friv*-**  * 

What  is  the  color  ?      f^r^r^J^  ' 

In  what  state  must  the  iodine  be  to  give  the  test  with  carbon  disul- 
phide ? 


(c?)   Replacement  of  iodine  by  other  halogens. 

To  about  3  cc.  of  a  very  dilute  solution  of  potassium  iodide, 
add  a  few  drops  of  chlorine  water. 
Result  f 


128  LABORATORY  EXERCISES 

Add  chloroform  (or  carboh  disulphide)  and  shake  the  mix- 
ture. 

Result  ? 

Complete  the  equation : 

Ki  +  cu-^AV+    .7. 

To  another  portion  of  potassium  iodide  solution,  add  bromine 
water  and  chloroform.     Shake  the  mixture. 
Result  f  L  .      &/ 

•      L/' 

Complete  the  equation : 

*   KI+Br2— ^JS_      + 


Under  what  conditions  does  one  element  replace  another  9     (See 
Experiment  27  and  the  table  it  contains.)  .  j^J^  c_ 

\n«(  tf  <ft**  *'"&***-   Vvr.t'-t^ 

Which   of  the  halogens  gives  the  greatest  heat  of  formation  in 
forming  compounds  with  a  given  element  f 

Which  gives  least  ?J^-06!-nA 

Which  of  the  halogens  is  most  easily  replaced  by  other  members  of 
the  family  f   £f-< 

Which  is  least,  easily  replaced  ? 

Arrange  the  halogens  in  the  order  of  their  replacing  power. 


THE  HALOGEN  ACIDS  129 

EXPERIMENT   48 

The  Halogen  Acids 

APPARATUS.     Three  test  tubes  ;  test  tube  rack  ;  bunsen  burner. 
MATERIAL.     Sodium  chloride  ;  sodium  or  potassium  bromide  ;  sodium 
or  potassium  iodide  ;  concentrated  sulphuric  acid  ;  blue  litmus  paper. 


(a)  To  1  gram  sodium  chloride  in  a  test  tube,  add  a  few 
drops  of  concentrated  sulphuric  acid.     Warm  gently. 
Result  ?         'uAjL 

Bring  a  strip  of  moist  litmus  to  the  mouth  of  the  test  tube. 
Result?     ;        ^ 

Blow  across  the  mouth  of  the  test  tube  and  notice  the  fum- 
ing of  the  gas  with  the  moisture  of  the  breath.  The  amount 
of  the  fuming  roughly  indicates  the  quantity  of  the  acid  issuing 
from  the  tube. 

If  hydrogen  chloride  were,  unstable,  into  what  two  elements  would 

it  decompose  ? 

What  would  be  the  color  of  such  a  mixture  of  gases  ? 

Do  you  find  this  color  in  the  test  tube  in  which  you  generated  the 
hydrochloric  acid  f 

What  is  your  decision  as  to  the  stability  of  this  acid  ? 

Write  the  equation  for  its  preparation. 

A  "         .->  tUW--t  ^ 

(5)  To  1  gram  of  potassium  bromide  in  a  test  tube,  add  a  few 
drops  of  concentrated  sulphuric  acid.  Warm  gently,  if  neces- 
sary. 

Result?    -^ 


130  LABORATORY  EXERCISES 

Test  the  gas  with  moist  litmus. 
Result  ? 

Complete  the  equation : 

NaBr  +  H2S04— ^NaaSO4 

What  is  the  color  of  the  gas  in  the  test  tube  9      /., 

Wfiat  element  gives  this  color  and  what  does  it  indicate  as  to  the 
stability  of  the  hydrobromic  acid  9 

Smell  the  gas  very  cautiously. 

you  detect  the  odor  of  sulphur  dioxide  ? 


Of  what  acid  is  sulphur  dioxide  the  anhydride  ? 

What  name  is  given  to  the  process  by  which  sulphuric  acid  is  con- 
verted into  sulphurous  acid  9  :  ^^tn^ 
Complete  the  equation : 

'     H2SO4  +  2HBr — ^H2SO3  +  _   _+_ 

/        .  -v       X  }      1       f       f\  ^*)  ""^   /  /\ 

Where  did  the  free  bromine  come  from  in  this  experiment  9 

(e)    To  1  gram  of  potassium  iodide  in  a  test  tube  add  a  few 
drops  of  concentrated  sulphuric  acid. 

Test  the  gas  with  litmus  and  determine  amount  of  fuming, 
as  before. 
Results  9 

What  do  these  results  show  about  the  amount  of  hydriodic  acid 
issuing  from  the  tube  ? 


THE  HALOGEN  ACIDS 


131 


Compare  the  stability  of  this  acid  with  that  of  hydrobromic  acid. 


Smell  the  gas  cautiously. 

Result  f 


teolterti*"^ 

Wliat  process  would  form  hydrogen  sulphide  from  sulphuric,  acid  f 


State  how  this  is  accomplished  by  the  hydriodic  acid,  accounting 
for  the  production  of  the  iodine  at  the  same  time.  (Compare  with 
action  of  sulphuric  acid  on  potassium  bromide.) 


DW-M 

Complete  the  equations: 


8NaI+ 

if  H2S04  +  8  HI 


; 


Which  of  these  three  halogen  acids  is  most  stable  ? 

l^L* 

Which  has  the  greatest  heat  of  formation  (see  table  below)  ? 

' 

Which    is  the  most  easily  oxidized   by  sulphuric  acid  f     Give  a 
reason  for  your  last  answer. 

fit&ehxsvt^  -     / 
7- 

HEATS   OF   FORMATION  OF   THE   HALOGEN   ACIDS 


Hydrochloric  acid 
Hydrobromic  acid 
Hydriodic  acid 


+  22,000  calories 
4-  8,400  calories 
—  7,000  calories 


132 


LABORATORY  EXERCISES 


EXPERIMENT   49 

Destructive  Distillation 

APPARATUS.  Hard  glass  test  tube  ;  two  sets  of  stoppers  and  delivery 
tubes,  as  shown  (Figure  41 );  two  8  in.  test  tubes  ;  ring-stand  ;  clamp  ; 
bunsen  burner. 

MATERIAL.     Wood  (splinters)  ;  soft  coal ;  litmus  paper. 

(a)   Destructive  distillation  of  wood. 

Arrange  apparatus  as  shown  (Figure  41),  having  the  lower 
end  of  the  delivery  tube  half  an  inch  from  the  bottom  of  the 

condensing  tube.  Fill  a  hard  glass 
test  tube  with  splinters  of  wood. 
Heat,  gently  at  first  and  then 
strongly,  until  no  further  change 
can  be  noted. 

Describe  the  appearance  of  the 
volatile  matter  passing  off  from  the 
wood. 

*    \j  C!"l/'V '" 

While  heating,  bring  a  flame  to 
the  end  of  the  jet  tube. 
Result  f 


Figure  41. 
What  is  the  substance  found  there  ? 


When  the  action  is  complete, 
allow  the  apparatus  to  cool,  then 
examine  the  contents  of  the  test 
tube.  J 


.c/ 


How  does  it  differ  from  the  original  wood  ? 


9/'ifr. 


DESTRUCTIVE  DISTILLATION  133 

What  is  the  appearance  of  the  substance  in  the  condensing  tube  ? 

/ 
Describe  any  distinct  layers  that  can  be  distinguished. 

^S^V     <&t<&t,l  idt 

' 
Test  the  liquid  in  the  condensing  tube  with  litmus  paper. 

Result  ?      ,&xA^ 


Note  the  odor  of  the  liquid.     & 


This  tarry  distillate  is  a  mixture  called  pyroligneous  acid. 
It  contains  wood  alcohol,  acetic  acid,  acetone,  tar,  and  other 
substances. 

The  decomposition  by  means  of  heat  of  a  complex  substance 
such  as  wood,  into  simpler  substances,  some  of  which  are  con- 
densed to  liquids,  is  called  destructive  distillation. 

Name  three  direct  products  of  the  destructive  distillation  of  wood. 


(5)   Destructive  distillation  of  coal. 

Free  the  hard  glass  tube  from  charcoal,  and  half  fill  it  with 
finely  crushed  soft  coal.  Replace  the  condenser  and  tubes  with 
a  fresh  set,  and  heat  as  before. 

Describe  the  appearance  of  the  volatile  matter  in  this  case. 

/  es,\*jL  -  -    /^y-tfov-CsC* 

• 

Is  it  the  same  as  that  obtained  from  the  wood  ? 

While  the  heating  is  going  on,  lay  a  piece  of  red  litmus  paper 
over  the  end  of  the  jet  tube. 
Result  ? 


What  kind  of  a  compound  is  shown  to  be  present  by  this  test  ? 

' 


134 


LAB  OR  A  TOR  Y  EXER  CISEti 


Bring  a  flame  to  the  end  of  the  jet  tube, 
Result  ? 

Heat  the  tube  until  gas  is  no  longer  given  off.  Then  allow 
the  tube  to  cool.  When  you  can  handle  the  hard  glass  tube, 
pour  its  solid  contents  on  the  base  of-  the  ring-stand. 

Describe  the  residue  as  to  color,  structure,  and  weight,  as  compared 

ivith  the  original  coal. 


This  residue  is  coke. 
Examine  the  condensing  tube. 

Describe  the  liquid  deposited  there. 

Jjrfipw      ts^tU-i^A-^  Mt&t-  '  t 

sUyUt  M     (>drvv<~          I 

Why  is  the  distillation  of  soft  coal  a  destructive  distillation  ? 


Name  three  direct  products  of  this  destructive  distillation. 


DRAWING 


PROPERTIES  OF  CARBON 


135 


EXPERIMENT   50 
Properties  of  Carbon 

APPARATUS.     Hard  glass  test  tube,  6",  with  one-hole  stopper  and  bent 

delivery  tube ;  two  test  tubes ;  beaker,  200  cc. ;  evaporating  dish  ; 

funnel ;  ring- stand  with  clamp,  and  one  ring  to  support  the  funnel ; 

stirring  rod  ;  bunsen  burner  ;  small  sheet  of  paper. 
MATERIAL.     Copper  oxide,  powdered  ;  charcoal,  powdered  ;  limewater  ; 

boneblack ;  sugar ;  copper  sulphate  solution,  1  to  40 ;  filter  paper ; 

cider  vinegar. 

(a)   Carbon  as  a  reducing  agent. 

Arrange  the  apparatus  as  shown  in  Figure  42.  Fill  one- 
tenth  of  a  test  tube  with  copper  oxide,  then  pour  the  oxide 
on  a  sheet  of  paper.  Using 
the  same  test  tube,  measure 
an  equal  volume  of  powdered 
charcoal.  Add  the  charcoal 
to  the  copper  oxide  on  the 
piece  of  paper,  and  mix  the  two 
thoroughly.  -Pour  the  mix- 
ture into  the  hard  glass  test 
tube  shown  in  the  figure. 
Pour  limewater  into  the  test 
tube  into  which  the  delivery 
tube  extends  until  the  lime- 
water  just  touches  the  end  of 
the  delivery  tube. 

Heat  the  hard  glass  test 
tube,  cautiously  at  first,  com- 
mencing at  the  part  around 
the  upper  portion  of  the  mix- 
ture, and  gradually  moving  the  flame  toward  the  closed  end  of 
the  tube. 


Figure  42. 


What  change  do  you  observe  in  the  limewater  at  first  ? 

'     ' 


136  LABORATORY  EXERCISES 

Carbon  dioxide  is  the  anhydride  of  carbonic  acid. 
Complete  the  equation  : 


What  base  is  in  solution  in  limewater  ? 


1  /  •  // 

:-&/..:  4  / 


Write  the  equation  for  the  neutralization  of  this  base  with  carbonic 

'acid-     &>  ^   £w 

2.  «j 

Allow  the  tube  to  cool,  and  when  cold  pour  its  contents  into 
a  200  cc.  beaker.  Let  a  small  stream  of  water  flow  into  the 

beaker. 

II  r  -fit 

What  substance  is  carried  away  by  the  water  f 

What  is  left  in  the  beaker  9 

What  element  is  taken  from  the  copper  oxide  f 

Complete  the  equation  : 

CuO+  C—  ^_   ^  +  ^ 

/-*• 

What  name  is  given  to  the  process  of  removing  oxygen  from  a    . 
compound  ?    , 

What  kind  of  an  agent  is  carbon  in  this  case  f 

(5)   Carbon  as  a  decolorizer. 

Thoroughly  mix  a  little  boneblack  with  some  cider  vinegar 
in  an  .evaporating  dish.  Fold  a  sheet  of  filter  paper  and  place 
it  in  the  funnel.  Pour  boneblack  on  the  filter  and  scoop  out  a 
hollow  in  the  center  of  the  boneblack.  Into  this  hollow, 
pour  the  mixture  of  vinegar  and  boneblack.  Collect  the  fil- 
trate and  note  its  color. 
Result? 

Put  enough  sugar  into  a  test  tube  to  fill  the  rounded  part. 
Heat  this  slowly  and  evenly,  rotating  the  tube  as  the  sugar 
melts.  The  sugar  should  be  well  browned,  but  not  burned. 
The  product  contains  caramel,  a  substance  used  as  a  flavor  in 


PROPERTIES  OF  CARBON  137 

cooking.  As  soon  as  the  tube  containing  the  caramel  has 
cooled,  fill  two  thirds  of  it  with  water,  and  warm  the  mixture 
until  the  solid  has  dissolved.  The  solution  thus  obtained  is 
used  to  illustrate  the  impure  sugar  solution  of  a  sugar  refinery. 
The  heat  used  in  obtaining  crude  sugar  helps  to  give  the 
product  a  brown  color  which  must  be  removed  to  get  white 
sugar. 

Filter  the  solution  of  sugar  and  caramel  as  you  did  the  cider 


Filter  a  dilute   solution  of  copper   sulphate  through  bone- 
black. 


Result?    /Zf>     ^L^VV^A 


Can  the  color  be  removed  from  all  liquids  by  filtering  them  through 
boneblack? 


DRAWING 


138 


LABORATORY  EXERCISES 


EXPERIMENT   51 

Preparation  and  Properties  of  Carbon  Dioxide 

APPARATUS.  Wide-mouth  battle,  8  oz.,  with  two-hole  rubber  stopper 
to  fit,  carrying  thistle  tube  and  delivery  tube  ;  three  wide-mouth  bot- 
tles ;  three  test  tubes  ;  glass  tube  ;  enamelled  ware  dish  or  pneumatic 
trough  ;  three  glass  plates. 

MATERIAL.  Marble  chips ;  concentrated  hydrochloric  acid  ;  limewater ; 
blue  litmus  solution  ;  candle  ;  wood  splinter. 


Figure  43. 


(a)   Preparation. 

Into  a  bottle  provided  with 
a  delivery  tube  and  a  thistle 
tube  reaching  nearly  to  the 
bottom  of  the  bottle,  put 
marble  chips  to  about  the 
depth  of  an  inch.  Cover 
the  marble  with  water,  and 
add  concentrated  hydro- 
chloric acid,  a  few  cubic  cen- 
timeters at  a  time,  so  as  to 


get  a  moderate  action.     Collect  three  bottles  of  the  gas  by  the 
displacement  of  water  (Figure  43)  for  use  in  parts  (#),  (5), 
,  and  (e). 
Describe  the  action  in  the  generator. 


Complete  the  equation: 
CaCO  *  HC1 


Write  the  equation  for  the  decomposition  of  carbonic  acid. 
Represent  the  entire  action  by  one  equation. 

,      -f  iktt-^&Alii  ^r  £*. 

Is  carbonic  acid  stable  at  ordinary  temperatures  ? 


PREPARATION  AND  PROPERTIES  OF  CARBON  DIOXIDE     139 

Why  can  any  of  the  common  acids  be  used  in  preparing  carbon 
dioxide  ?    . 


(5)  Odor  and  color. 

Inhale  some  of  the  gas  from  a  bottle. 
WJiat  is  the  effect  of  the  gas  on  the  nose  ? 

Has  carbon  dioxide  color  ? 
(e)   Solubility. 

Let  the  gas  from  the  generator  bubble  through  a  test  tube 
half  full  of  blue  litmus  solution. 
What  change  takes  place  ?  J?-/ 

(If  the  result  is  not  evident  to  you,  compare  the  color  of  the 
liquid  in  the  test  tube  with  that  of  the  litmus  solution  in  the 
stock  bottle.) 

Why  is  carbon  dioxide  called  an  acid  anhydride  ? 

Write  the  equation  for  the  reaction  of  carbon  dioxide  with  water. 

' 

What  does  the  method  of  collection  shoiv  in  regard  to  the  extent  to 


which  carbon  dioxide  is  soluble  in  water  ?  ^^frCsfrfM 

How  is  the  solubility  of  the  gas  increased  in  the  preparation  of 
effervescent  drinks  ?     (Class  discussion.}    $ .  \ ,_ 

7    g 

Relative  weight  and  relation  to  combustion. 
Slowly  invert  a  bottle  of  carbon  dioxide  over  a  lighted  candle. 

Results? 

-^£^; 


What,  three  properties  of  carbon  dioxide  are  shown 

Vt/t-Q' 


140  LABORATORY  EXERCISES 

(e)  Action  with  limewater. 

Pour  half  a  test-tubeful  of  limewater  into  a  bottle  of  carbon 
dioxide  and  shake  the  bottle. 

Result  t 

/ 

Write  the  equation  to  show  the  formation  of  the  precipitate,  calcium 
carbonate. 

&&(OI4)     r/-  —7        60-     ^^^     **t~ 

(/)  Product  of  combustion. 

Burn  a  wooden  splinter  in  a  bottle  of  air.     Add  limewater 
and  shake  the  bottle. 
Result  f 

How  does  this  show  that  the  splinter  contains  carbon  ?. 

* 


Blow  through  a  glass  tube  into  a  test  tube  half  full  of  lime- 
water. 

EesuU? 

';          ./:,-x, 

What  gas  do  we  exhale  9 

o  /-•;••' 

How  is  it  produced  in  the  body  ? 

<r. 
f!^  ,   <w> 

' 


CHEMICAL   FIRE  EXTINGUISHER  141 

EXPERIMENT   52 

Chemical  Fire  Extinguisher 

APPARATUS.  Four  test  tubes,  6" ;  one-hole  rubber  stopper  to  fit  test 
tubes  and  carrying  a  delivery  tube ;  wide-mouth  bottle,  6  oz. ;  test 
tube,  4"  x  y ;  one-hole  rubber  stopper  to  fit  6  oz.  bottle ;  glass 
tube  4"  long ;  glass  tube  2"  long  drawn  out  so  as  to  deliver  a  stream 
2  mm.  in  diameter;  2'  of  rubber  tubing  to  fit  glass  tubes;  bunsen 
burner ;  ring- stand  with  small  clamp  ;  pan. 

MATERIAL.  Limewater  ;  sodium  bicarbonate  ;  sulphuric  acid,  1  to  10; 
splinters  of  wood. 

(a)  Pour  15  cc.  of  limewater  into  a  test  tube  and  set  it  aside 
for  future  use.  Close  the  mouth  of  another  test  tube  with  a 
one-hole  rubber  stopper  carrying  a  delivery  tube.  Arrange 
the  apparatus  so  that  the  delivery  tube  will  dip  into  the  lime- 
water  in  the  first  test  tube. 

Pour  into  the  test  tube  generator  enough  sodium  bicarbonate 
to  fill  the  curved  portion  of  the  test  tube ;  add  about  10  cc. 
of  water  and  a  few  drops  of  sulphuric  acid,  then  immediately 
replace  the  stopper. 

What  is  the  name  of  the  gas  evolved  ? 
Complete  the  equation  : 

2  NaHC03  +  H2S04— >- +  ; +  _ 

(&)  Arrange  the  apparatus  as  nrpart  (a),  using  a  dry  test 
tube  for  the  generator.  Pour  into  the  test  tube  generator  about 
5  cc.  of  sodium  bicarbonate  and  heat  it  until  the  flame  in  con- 
tact with  the  test  tube  turns  yellow.  This  indicates  that  the 
glass  is  beginning  to  soften.  Continued  heating  would  melt 
the  glass. 

What  change  takes  place  in  the  limewater  ? 

What  collects  on  the  cool  portion  of  the  tube  f 


142 


LABORATORY  EXERCISES 


What  are  two  of  the  substances  produced  by  the  decomposition  of 
sodium  bicarbonate  ? 


Complete  the  equation : 
2  NaHCO3— 


Figure  44. 


Why  is  sodium  bicarbonate  the 
chief  ingredient  of  dry-powder  Jire 
extinguishers  ? 


(c)  Arrange  apparatus  as  shown 
in  Figure  44.  Pour  a  nearly  satu- 
rated solution  of  sodium  bicarbon- 
ate into  the  wide-mouth  bottle  until 
the  surface  of  the  liquid  reaches 
the  curved  portion  of  the  bottle 
near  its  neck.  Fill  the  small  test 


tube  with  very  dilute  sulphuric  acid  (1  to  10)  and  stand  the 

test  tube  in  the  bottle. 

Replace  the  stopper  and 

set    the    bottle   on   the 

table. 

Build  a  small  fire  of 
splinters  of  wood  in  a 
pan  placed  in  a  sink,  or 
wherever  tha  instructor 
may  direct.  Hold  the 
stopper  of  the  fire  ex- 
tinguisher firmly  pressed 
into  the  mouth  of  the 
bottle  (Figure  45); 
point  the  end  of  the 


Figure  45. 


delivery  tube»at  the  fire,  and  invert  the  bottle, 
fire. 


Put  out  the 


CHEMICAL   FIRE  EXTINGUISHER  143 

What  gas  was  generated  by  the  reaction  between  the  sodium  bicar- 
bonate and  the  sulphuric  acid  ? 

Why  was  the  liquid  forced  out  of  the  bottle  ?     /- 

L^     £ 


What  two  advantages  are  there  in  using  more  than  enough  sodium 
bicarbonate  to  neutralize  the  sulphuric  acid  ! 


Piw 

144  LABOEATOEY  EXEECISES 

r~  v      h£7 
EXPERIMENT   53 

Hard  Waters 

APPARATUS.  Carbon  dioxide  generator,  consisting  of  wide-mouth  bottle 
with  two-hole  stopper  to  fit,  carrying  thistle  tube  and  delivery  tube  for 
leading  gas  to  the  bottom  of  a  test  tube ;  four  test  tubes ;  small 
funnel ;  stirring  rod  ;  bunsen  burner. 

MATERIAL.  Calcium  sulphate  (plaster  of  Paris) ;  magnesium  sulphate  ; 
marble  chips ;  dilute  hydrochloric  acid,  1:4;  limewater ;  distilled 
water  ;  filtered  soap  solution  ;  filter  paper. 

(a)  Add  a  drop  or  two  of  soap  solution  to  distilled  water  in 
a  test  tube  and  shake  the  tube. 

Are  lasting  suds  produced  ? 

This  result  is  characteristic  of  "  soft "  waters. 
Drop  a  pinch  of  magnesium  sulphate  into  a  test  tube  two 
thirds  full  of  water.      Close  the  mouth  of  the  tube  with  the 
thumb  and  shake  it  thoroughly.     Add  a  few  drops  of  the  soap 
solution.     Shake  the  tube. 
Do  suds  form  ? 
What  is  produced  f 

flu  n^  *{<!        ''*  "'•     £*'  '  '   • 

/ 

This  is  an  insoluble  magnesium  soap.     Waters  that  behave 
in  this  way  with  soap  solution  are  "  hard  "  waters. 

Continue  the  addition  of  soap  solution  until  suds  finally  form. 
Why  does  it  cost  more  to  wash  with  hard  water  than  ivith  soft 

water 

#;( 


What  would  tend  to  become  entangled  in  the  fibers  of  a  fabric 
when  clothes  are  washed  with  hard  water  9 


(b)  Put  some  pieces  of  marble  into  a  generator  and  cover 
them  with  dilute  hydrochloric  acid.     Lead  the  carbon  dioxide 

U  M-  V  N  Ci  ->  Ca 


HARD    WATERS  145 

formed  to  the  bottom  of  a  test  tube  two  thirds  full  of  lime- 
water.        Otfu(j?/fj^ 

What  is  the  first  Result  f 

The  insoluble  compound  formed  is  calcium  carbonate. 
Write  the  equation  for  its  precipitation.  //  ,  /% 


What  happens  to  the  precipitate  on  the  continued  passing  of  the 
carbon  dioxide  ?  ^2^y  O^n.  OL^<  »     Qf.  fy> 

. 

The  compound  formed  is  calcium  bicarbonate, 

7s  it  soluble  or  insoluble  ? 

What  acid  was  formed  when  the  excess  of  carbon  dioxide  reacted 
with  the  water  in  the  test  tube  ?  /&.  6-  0  o      (l/fa/d^W*^     0~4JLA 

What  effect  did  this  acid  have  on  the  precipitate,  calcium  carbonate  ? 
Complete  the  equation  : 

,0.       A>1^  /)  t*L  /]  ft*.  If  /ft     /)       \ 

CaCUo  -f-            •'.-••  i.  ^4-    '^      U     — >• 
Y  3-t  ,;-r     2T^- 

(c)  Pour  a  little  of  the  water  solution  of  calcium  bicarbonate 
into  another  test  tube.  To  this  portion,  add  a  few  drops  of 
soap  solution  and  shake  the  tube. 

What  kind  of  water  is  the  water  containing  calcium  bicarbonate  in 


solution?  >'   ;    y.    .sfifrs^uu    X/'r^ 

4s*^  *rW**J. 


In  a  separate  test  tube  heat  gently  another  portion  of  t 
calcium  bicarbonate  solution. 

What:  happens  on  warming  the  liquid,  particularly  near  the  watts 
of  the  test  tube?  £/  x 

Hold  a  stirring  rod  with  a  drop  of  lime  water  on  its  end  above 
the  heated  liquid  in  the  test  tube. 
What  is  the  effect  on  the  limewater  ? 

*+&*-*  ^<u>^ 


146  LABORATORY  EXERCISES 

What  does  this  show  ?       <£&£ 


Continue  heating  the  liquid  in  the  test  tube  until  it  boils. 

What  is  the  second  effect  of  heat  on  a  woJer  solution  of  calcium 
bicarbonate  ? 

b     A  •'V;   A"  ,  Y       ,'t'X'W  *!».<    sff'fv'     ^// 

Filter  the  contents  of  the  tube  just  heated.     Test  the  filtrate 
with  a  few  drops  of  soap  solution. 

Has  the  water  solution  of  calcium  bicarbonate  been  softened  ? 
Explain. 

Such  a  hard  water  is  called  a  "temporary"  hard  water. 

Complete  the  equation  for  the  softening  of  a  temporary  hard  water 
by  boiling: 

CaHjCCOi),— *-< 


Account  for  the  crust  formed  on  the  inside  of  tea  kettles  in  tvhich 
temporary  hard  water  is  boiled  day  after  day. 


(d)  Add  a  pinch  of  calcium  sulphate  (plaster  of  Paris)  to  a 

test  tube  two  thir'ds  full  of  water.     Shake  the  tube,  filter  the 

contents,  and  divide  the  filtrate  into  two  portions.     Using  one, 

determine  with  soap  solution  whether  or  not  the  water  is  hard. 

Kesult? 

Boil  the  second  portion,  and  then  test  with  soap  solution. 

ut  ^$fy,.f'  *       J//tyA''y^S' 
Is  the  water  solution  of  calcium  sulphate  softened  by  boiling  ?    / 


HARD   WATERS  147 


Such  water  is  "permanent"  hard  water. 
Would  permanent  hard  water  form  a  deposit  on  a  teakettle  f*& 

Explain,     c^i  j/j   M&frW&CSCt 


A  water  often  contains  both  temporary  and  permanent  hard- 

ness. 

How  could  you  show  the  presence  of  each  kind  of  hardness  in  the 
presence  of  the 


148 


LABORATORY  EXERCISES 


EXPERIMENT   54 

Baking  Powders 

APPARATUS.  Four  test  tubes  ;  rubber  stopper,  one-hole,  to  fit  test  tube 
and  carrying  a  delivery  tube  as  shown  in  Figure  46  ;  test  tube  rack. 

MATERIAL.  Sodium  bicarbonate  ;  limewater ;  hydrochloric  acid,  1  to  4  ; 
potassium  acid  tartrate  ;  monocalcium  phosphate ;  monosodium 
phosphate  ;  sodium  alum  ;  blue  litmus  paper. 


(a)  Reaction  between  sodium  bicarbonate  and 
acids. 

Arrange  apparatus  as  shown  in  Figure  46. 
Pour  about  10  cc.  of  limewater  into  the  test 
tube  into  which  leads  the  long  arm  of  the 
delivery  tube.  Remove  the  stopper  and 
put  a  pinch  of  sodium  bicarbonate  (baking 
soda)  in  the  tube  ;  add  a  few  drops  of  dilute 
hydrochloric  acid  and  immediately  replace 

Figure  46.  the  stopper. 

What  gas  is  liberated  by  the  reaction  ? 

Write  the  equation  representing  the  reaction. 

Sour  milk  contains  lactic  acid,  H(C3H5O3). 

Why  is  a  mixture  of  sour  milk  and  baking  soda  used  as  a  leaven- 
ing agent? 

Equation  ? 


(5)  Cream  of  tartar  baking  powders. 

Sprinkle  a  few  particles  of  cream  of  tartar,  potassium  acid 
tartrate,  KH(C4H4O6),  on  a  dry  piece  of  blue  litmus  paper. 
Result? 


BAKING  POWDERS  149 

Wet  the  powder  and  paper. 
Remit? 

Into  what  ions  would  potassium  hydrogen  tartrate  be  dissociated 
by  water? 

Equation  ? 

What  kind  of  ions  produced  the  action  on  the  litmus  paper? 

Mix  a  little  dry  cream  of  tartar  with  a  little  dry  baking  soda, 
and  pour  the  mixture  into  a  dry  test  tube  arranged  with  a  one- 
hole  stopper  carrying  a  delivery  tube  that  extends  into  some 
lime  water  in  another  test  tube.  Add  a  little  water  to  the 
mixture  of  cream  of  tartar  and  baking  soda,  and  immediately 
replace  the  stopper  carrying  the  delivery  tube. 
Result? 

Account  for  the  fact  that  carbon  dioxide  is  not  evolved  from  a  dry 
mixture  of  sodium  bicarbonate  and  potassium  acid  tartrate,  but 
is  generated  as  soon  as  the  mixture  is  wet. 


Complete  the  following  equation,  representing  the  reaction  that  takes 
place  in  the  presence  of  water : 

NaHCOg  +  KH(C4H406)  — >-  NaK(C4H4O6)  +  _        _+_ 

Cream  of  tartar  baking  powders  consist  of  a  mixture  of  cream 
of  tartar,  sodium  bicarbonate,  and  some  inert  substance,  such  as 
starch  or  flour,  which  is  used  as  a  filler. 

Calculate  the  number  of  grams  of  sodium  bicarbonate  that  would 

react  with  10  grams  of  potassium  acid  tartrate. 


150  LABORATORY  EXERCISES 

Wliat  volume  of  carbon  dioxide,  measured  at  standard  conditions, 
would  be  evolved  when  the  mixture  was  wet? 


What  volume  would  the  gas  occupy  at  21°  C.  and  a  pressure  of 
770  mm.  ? 


One  of  the  cream  of  tartar  baking  powders  is  prepared  by 
mixing  dry  2  parts  by  weight  of  cream  of  tartar,  1  part  of 
sodium  bicarbonate,  and  1  part  of  starch. 

(c?)  Phosphate  powders. 

Sprinkle     a     few     particles      of     monocalcium     phosphate, 
CaH4(PO4)3  on  a  wet  piece  of  blue  litmus  paper. 
Result? 

What  ion  derived  from  the  monocalcium  phosphate  produces  this 
change  9 

Repeat     the     experiment,     using     monosodium     phosphate, 
NaH2PO4,  in  place  of  monocalcium  phosphate. 
Account  for  the  reaction. 


BAKING  POWDERS  151 

Some  phosphate  baking  powders  consist  of  dry  mixtures  of 
monocalcium  phosphate,  sodium  bicarbonate,  and  a  filler ;  other 
phosphate  baking  powders  are  dry  mixtures  of  monosodium 
phosphate,  sodium  bicarbonate,  and  a  filler. 

(c?)   Alum  baking  powders. 

Sprinkle  a  few  particles  of  sodium  alum,  sodium  aluminum 
sulphate,  NaAl(SO4)2  on  a  wet  piece  of  blue  litmus  paper. 
Result? 

Sodium  aluminum  sulphate  is  a  double  salt,  consisting  of 
sodium  sulphate  in  combination  with  aluminum  sulphate.  Alu- 
minum sulphate  is  hydrolyzed  in  solution  (see  §  183,  First 
Principles  of  Chemistry). 

Write  an  equation  to  shoiv  this  hydrolysis. 


Why  does  a  water  solution  of  alum  give  an  acid  reaction? 


Alum   baking  powders   consist   of   dry   mixtures   of   alum, 
sodium  bicarbonate,  and  a  filler. 

Why  should  a  baking  powder  be  stored  in  an  air-tight  container? 


Should  a  baking  powder  be  mixed  with  the  flour  before  or  after  the 
addition  of  water? 

Why? 


152 


LABORATORY  EXERCISES 


EXPERIMENT   55 


Preparation  and  Properties  of  Carbon  Monoxide 

APPARATUS.  Ring-stand  with  1  ring  and  1  clamp ;  wire  gauze  with 
asbestos  center;  beaker,  200  cc.  ;  side  arm  test  tube,  with  single 
hole  rubber  stopper  to  fit ;  small  thistle  tube ;  delivery  tube  ;  en- 
ameled pan ;  two  wide- mouth  bottles,  4  oz. ;  glass  plate ;  bunsen 
burner. 

MATERIAL.  Formic  acid,  sp.  gr.  1.2;  concentrated  sulphuric  acid; 

limewater. 

(a)  Preparation. 

Arrange  the  apparatus  as 
shown  in  Figure  47.  Pour  5 
cc.  of  formic  acid  and  an  equal 
amount  of  concentrated  sulphu- 
ric acid  through  the  thistle  tube 
into  the  side  arm  test  tube. 
Heat  the  water  in  the  beaker 
until  it  boils.  Collect  the  gas 
in  small  bottles  as  long  as  it  is 

evolved.       Do  not  let  carbon  monoxide 
escape  into  the  room ;  it  is  very  poisonous. 


Figure  47. 


Get  rid  of  the  gas  in  any  of  the  bottles  that  you  do  not  need 
by  burning  it. 

(5)  Properties. 

Burn  a  bottle  of  carbon  monoxide. 

Describe  the  color  of  the  flame.  /£ 
. 

Compare  this  flame  with  that  of  burning  hydrogen. 


Pour  15  cc.  of  limewater  into  the  bottle  in  which  the  carbon 
monoxide  has  been  burned  and  shake  the  liquid  around  gently. 
Result?    & 


PREPARATION  OF  CARBON  MONOXIDE  153 

W/iat  gas  is  formed  by  the  burning  of  carbon  monoxide  f    /, 
Write  the  equation  for  this  reaction. 

(c)   General  questions., 

The  formula  of  formic  acid  is  HCHO2. 

Write  the  equation  for  its  decomposition. 

+  z  0   4-    L6  + 

Explain  how  concentrated  sulphuric  acid  helps  to  bring  about  this 
decomposition.    (~A  * 

/ 

C/0  ^w/' 


154  LABORATORY  EXERCISES 

EXPERIMENT   56 

Preparation  and  Properties  of  Carbon  Monoxide 
Second  Method 

APPARATUS.  Flask,  250  cc.;  two-hole  rubber  stopper  to  fit  flask,  pro- 
vided with  thistle  tube  ;  delivery  and  connecting  tubes  as  shown  in 
Figure  48;  two  wide-mouth  bottles,  6  oz.,  provided  with  two-hole 
rubber  stoppers  and  tubes  as  shown  in  the  figure ;  three  wide- 
mouth  bottles,  6  oz.  ;  pneumatic  trough  ;  glass  plate  ;  ring-stand 
with  1  ring  and  1  clamp  ;  wire  gauze  with  asbestos  center ;  bunsen 
burner ;  two  test  tubes ;  single  hole  rubber  stopper  to  fit  test  tube, 
provided  with  L  delivery  tube. 

MATERIAL.  Crystallized  oxalic  acid ;  concentrated  sulphuric  acid ; 
caustic  soda  solution,  300  g.  to  the  liter ;  limewater. 

Caution !    Concentrated  sulphuric  acid,  especially  when  hot,  produces  extremely 
serious  burns  ;  also  carbon  monoxide  is  very  poisonous. 

(#)   Preliminary  test. 

Put  a  pinch  of  oxalic  acid  in  a  test  tube  and  add  1  cc.  of 
concentrated  sulphuric  acid.  Fit  the  test  tube  with  a  rubber 
stopper  and  delivery  tube.  Into  a  second  test  tube  put  10  cc. 
of  limewater.  Heat  the  contents  of  the  first  tube  gently,  and 
allow  the  gas  that  is  given  off  to  pass  through  the  limewater 
in  the  second  tube. 
Result  ? 


What  gas  is  shown  as  one  of  the  products  of  the  action  between 
oxalic  and  sulphuric  acids  ? 

(5)  Preparation. 

Arrange  the  apparatus  shown  in  Figure  48.  Info  the  flask 
put  15  grams  of  oxalic  acid.  Into  each  of  the  two  wide-mouth 
bottles  put  30  cc.  of  caustic  soda  solution.  Make  sure  that 
the  tube  by  which  the  gas  enters  a  bottle  reaches  nearly  to  the 


PROPERTIES   OF  CARBON  MONOXIDE 


155 


bottom,  and  that  the  tube  by  which  the  gas  leaves  reaches  only 

just    below    the    rubber 

stopper.       The  thistle 

tube  should  reach  nearly 

to    the    bottom    of    the 

flask. 

Pour  about  20  or  30  cc. 
of  sulphuric  acid  through 
the  thistle  tube  into  the 
flask.  Heat  the  mixture 
with  a  small  flame. 
When  the  action  has 
started,  remove  the  flame, 
but  replace  if  the  action 
becomes  too  slow.  Collect  in  bottles  in  the  pneumatic  trough 
the  gas  that  is  given  off. 

Compare  the  rates  at  which  bubbles  pass  through   the  two   wash 
bottles. 

Why  are  two  bottles  of  caustic  soda  solution  necessary  9 


Figure  48. 


(tf)   Properties. 

As   soon  as  a  bottle  fills  with  the  gas,  remove  it  from  the 
trough  and  hold  its  mouth  to  the  flame. 
Why  did  the  first  bottles  fail  to  ignite  9 


Repeat  the  experiment,  using  a  second  bottle  of  the  gas. 
Describe  a  carbon  monoxide  flame  as  to  brightness  and  color. 

When  you  have  burned  a  bottle  of  carbon  monoxide,  pour 
into  it  20  cc.  of  limewater.     Shake  the  limewater  around  in 
the  bottle  gently  for  a  moment. 
Result  9 


156  LABORATORY  EXERCISES 

What  is  the  product  formed  when  carbon  monoxide  burns  f 
Write  the  equation  for  the  reaction.' 

(c?)   General  questions. 

What  two  gases  result  from  the  decomposition  of  oxalic  acid  by 
the  aid  of  sulphuric  acid  ? 

From  an  inspection  of  the  formula  of  oxalic  acid,  H2C204,  decide 
what  a  third  product  is. 

Explain  how  sulphuric  acid  produces  the  action. 


Write  the  equation  for  the  decomposition  of  oxalic  acid. 


What  happens  in  the  'wash  bottles  to  the  gas  that  was  shown  to  be 
present  in  part  (a)  9 


Write  an  equation  to  show  this. 


Why  might  the  flames  of  hydrogen  and  of  carbon  monoxide  be  con- 
fused 9 

How  could  you  distinguish  them  by  a  test  of  the  products  of  com- 
bustion 9 


BORAX  AND  BORIC  ACID  157 


EXPERIMENT   57 
Borax  and  Boric  Acid  ff*  $ 

/£  £      D;  5 

APPARATUS.     Beaker,  100  cc.  ;  stirring  rod;  funnel;  graduate,  50  cc.  ; 

evaporating  dish  ;  ring-stand  with  two  rings  ;  wire  gauze  with  asbes- 

tos center  ;  bunsen  burner  ;  balance  with  weights  ;  pan  of  cold  water  ; 

test  tube. 
MATERIAL.    Filter  paper;  borax;  sulphuric  acid,  concentrated  ;  alcohol; 

hydrochloric  acid,  1  to  4  ;  ammonia  water,  concentrated  ;  turmeric 

paper. 

(a)   Preparation  of  boric  acid. 

Weigh  out,  on  a  balanced  filter,  12  grams  of  borax.  Pour 
50  cc.  of  water  into  a  beaker  and  heat  it  to  boiling  on  a  wire 
gauze  placed  over  a  bunsen  flame.  Dissolve  the  borax  in  the 
hot  water.  Measure  out  6  cc.  of  sulphuric  acid  and  very 
slowly  pour  it  down  a  stirring  rod  held  just  above  the  solution 
of  borax,  so  that  the  acid  will  enter  the  solution  drop  by  drop. 

Cool  the  solution  by  setting  the  beaker  in  a  pan  of  cold  | 
water.  As  the  cooling  proceeds,  boric  acid  will  crystallize  out. 
Filter  the  mixture  and  wash  the  boric  acid  on  the  filter  three  or 
four  times.  Use  a  few  cubic  centimeters  of  cold  water  at  a 
time  and  allow  one  portion  of  water  to  run  through  the  filter 
before  adding  a  second  portion. 

What  is  the  formula  for  the  acid  of  which  borax,  Na^Oy,  is  a 


This  acid  combines  with  water  to  form  boric  acid,  H3BO3. 

Taking  these  facts  into  consideration,  write  equations  representing 
in  two  steps,  the  production  of  boric  acid  by  the  method  you  have 
employed.  Then  represent  the  reactions  by  a  single  equation. 


///»/-/    Z         A    - 


158  LABORATORY  EXERCISES 

Account  for  the  fact  that  the  reaction  runs  in  one  direction  (see 
Experiment  28). 

^•"  ';••/••"""  ......  ' 

Could  hydrochloric  acid  be  used  in  place  of  sulphuric  acid?    yC 
Why  do  you  think  so  ?     , 


What  by-product  was  left  in  the  liquid  from  which  the  boric  acid 
crystallized  ? 

Why  were  better  results  obtained  by  repeatedly  washing  the  boric 
acid  than  could  have  been  obtained  by  using  the  same  quantity  of 
ivash  water  at  one  time  f 


(5)   Alcohol  test  for  boric  acid. 

Place  some  of  the  boric  acid  you  have  prepared  in  an  evapo- 
rating dish  and  just  cover  it  with  alcohol.    Set  fire  to  the  alcohol. 
What  color  of  the  Jlame  in  addition  to  yellow  do  you  observe  f 

X    '      '  C^"-—         . 

Treat  a  little  borax  in  the  same  manner  that  you  have  just 
treated  the  boric  acid. 

Hoiv  does  this  Jlame  differ  in  color  from  the  preceding  flame  9 

(tf)   Turmeric  test  for  boric  acid. 

Dip  a  piece  of  turmeric  paper  in  a  solution  of  boric  acid  and 
then  dry  the  jfeper  by  wrapping  it  around  a  test  tube  containing 
boiling  water. 

O/   // 
What  change  in  the  color  of  the  turmeric  do  you  observe  ? 

Add  to  the  paper  a  little  ammonium  hydroxide. 
What  change  in  color  do  you  observe  ? 


BORAX  AND  BORIC  ACID  159 

Determine  whether  dilute  hydrochloric  acid  will  restore  the 
color  of  turmeric  paper  after  it  has  been  changed  by  boric  acid 
and  ammonium  hydroxide. 

Besult?     i   £t£tt44L  >^£ 


Test  for  borax. 

Acidulate  a  solution  of  borax  with   hydrochloric   acid   and 
make  the  turmeric  paper  test  for  boric  acid. 


» 


160  LABORATORY  EXERCISES 

EXPERIMENT   58" 

Water  Softening 

APPARATUS.     Dropping   bottle   with   notched  cork;   funnel;   four  test 

tubes  ;  bunsen  burner. 
MATERIAL.     Calcium  sulphate  (plaster  of  Paris)  ;  magnesium  sulphate  ; 

temporary  hard  water  ;  limewater  ;  sodium  carbonate  solution  ;  fil- 

tered soap  solution  ;   filter  paper. 

(&)  Boil  one  third  of  a  test  tube  of  temporary  hard  water. 

Result? 

/ 

*/  $  y  ?>/ 

How  does  the  boiling  soften  the  water? 

t/ufrbi      ffe-,  & 

Complete  the  equation  : 

CaH2(C08)2—  »-_  .  +  .  _  +  . 


What  becomes  of  the  substance,  that  causes  the  hardness  ? 


Temporary  hard  waters,  before  being  fed  to  boilers,  are  some- 
times brought  to  boiling  in  a  feed  water  Beater. 
Why  ? 

Why  is  the  water  then  filtered  before  passing  it  into  the  boiler 
where  steam  is  generated  f 

(6)  To  one  third  of  a  test  tube  of  temporary  hard  water  add 
an  equal  volume  of  limewater. 

Result  ? 

Write  the  equation  for  the  action  of  limewater  on  the  temporary 
hard  water. 


WATER   SOFTENING  161 

What  acid  must  be  in  excess  when  calcium  bicarbonate  is  formed  ? 

Write  the  equation  for  the  neutralization  of  this  acid  with  lime- 
water. 

Which  product  is  the  precipitate  f 
How  is  limewater  made  ? 


Why  is  lime  added  to  tanks  of  temporary  hard  water  in  a  water- 
softening  plant  ? 


(c)  Prepare  a  permanent  hard  water  by  shaking  a  pinch  of 
calcium  sulphate  (plaster  of  Paris)  in  a  test  tube  of  water  and 
then  filtering  the  liquid.  Pour  half  of  this  hard  water  into 
another  test  tube  and  set  it  aside  for  later  use. 

To  the  other  half  of  the  hard  water,  slowly  add  a  sodium  car- 
bonate solution  from  a  dropping  bottle,  as  long  as  any  precipi- 
tate forms.  Shake  the  tube  after  each  addition  of  the  carbonate. 
Write  the  equation  for  the  reaction. 


Which  of  the  two  products   do  you  know   to   be  an   insoluble 
substance  ? 

Remove  the  precipitate  from  the  liquid  by  filtering.      Test 
the  filtrate  with  soap  solution  to  determine  the  readiness  with 
which  it  forms  permanent  suds. 
ResuU  f 

Similarly  try  the  soap  solution  with  the  portion  of  the  orig- 
inal hard  water  that  was  set  aside. 

Which  forms  suds  more  readily,  the  original  hard  water,  or  the 
water  to  which  sodium  carbonate  was  added  ? 


162  LABORATORY  EXERCISES 


Take  half  a  test  tube  of  temporary  hard  water  and  add 
to  it  a  pinch  of  calcium  sulphate  and  a  pinch  of  magnesium 
sulphate.  Add  water  to  fill  the  test  tube  and  mix  the  contents 
by  shaking.  If  the  liquid  is  not  clear,  filter  it.  This  repre- 
sents a  common  type  of  hard  water  that  contains  several  causes 
of  hardness. 

To  the  hard  water  add  limewater,  a  few  drops  at  a  time,  as 
long  as  a  precipitate  forms.  Filter  the  liquid.  To  the  filtrate 
add  sodium  carbonate  solution  from  the  dropping  bottle  as  long 
as  precipitation  occurs. 

Filter  the  liquid  and  test  the  filtrate  with  soap  solution. 

Result  ? 


Was  the  hardness  due  to  magnesium  removed  from  the  water  by 
the  lime  and  soda  treatment  (i.e.  limewater  and  sodium  carbonate)? 


BLEACHING   OF  COTTON  163 

(cV   £•*• 
EXPERIMENT   59 

Bleaching  of  Cotton 

APPARATUS.  Porcelain  mortar  and  pestle;  1000  cc.  graduate;  two 
beakers,  250  cc. ;  glass  stirring  rods;  ring-stand  with  ring;  wire 
gauze  with  asbestos  center ;  burisen  burner. 

MATERIAL.  Unbleached  cotton  waste  ;  litmus  paper  ;  solutions  prepared 
as  directed  below ;  bleaching  powder ;  sodium  hydroxide ;  sodium 
thiosulphate  ;  concentrated  sulphuric  acid  ;  starch  ;  sodium  iodide. 

Preparation  of  Solutions.  The  quantities  given  are  sufficient  for  a  class 
of  ten  pupils. 

Alkali.     Dissolve  16  g.  of  sodium  hydroxide  in  1000  cc.  of  water. 

Bleaching  Solution.  Work  10  g.  of  a  good  quality  of  bleaching  powder 
into  a  smooth,  thin  paste  with  a  little  water  in  a  porcelain  mortar.  Rinse 
the  paste  into  a  1000  cc.  graduate,  and  then  add  water  until  the  graduate 
is  filled  to  the  800  cc.  mark.  Pour  the  mixture  into  a  bottle,  shake  it  thor- 
oughly, and  then  allow  the  undissolved  matter  to  settle.  Use  only  the  clear 
supernatant  liquid. 

Acid.     Pour  30  cc.  of  concentrated  sulphuric  acid  into  500  cc.  of  water. 

Antichlor.  Dissolve  2  g.  of  sodium  thiosulphate  ("hypo")  in  500  cc.  of 
water. 

Starch  Iodide  Paste.  Mix  some  starch  with  cold  water  and.  slowly  pour 
the  mixture  into  50  cc.  of  boiling  water.  Stir  constantly  and  discontinue 
the  addition  of  starch  and  the  boiling  as  soon  as  a  thin  paste  has  been  ob- 
tained. Add  5  cc.  of  a  dilute  solution  of  sodium  iodide  to  the  starch  paste 
and  mix  the  two  thoroughly  by  stirring. 

(a)  Cotton  yarn  and  cloth  are  "  boiled  out "  to  remove  wax, 
grease,  and  dirt  which  would  prevent  the  uniform  action  of  the 
bleach  on  the  fibre. 

Pour  100  cc.  of  the  alkali  solution  into  a  200  cc.  beaker  and 
immerse  in  the  liquid  about  a  gram  of  cotton  waste.  Heat  the 
liquid  to  boiling,  and  continue  to  boil  it  gently  for  10  minutes, 
meanwhile  keep  the  cotton  in  motion  in  the  liquid  by  means  of 
a  stirring  rod. 

What  evidence  is  there  that  substances  have  been  removed  from  the 
cotton  f 

Remove  the  waste  and  rinse  it  repeatedly  in  water. 


164  LABORATORY  EXERCISES 

(6)  Pour  50  cc.  of  the  bleaching  solution  into  a  beaker  and 
put  the  wet  cotton  waste  into  it.  By  means  of  a  glass  rod, 
work  the  cotton  in  the  liquid  for  at  least  five  minutes  and  then 
allow  it  to  remain  in  the  liquid  another  five  minutes. 

(<?)  Remove  the  waste  from  the  bleaching  solution  and,  with- 
out rinsing  it,  put  it  into  a  beaker  containing  50  cc.  of  the 
acid  and  work  it  in  the  liquid  for  five  minutes. 

Acids  react  with  bleaching  powder  to  produce  a  calcium  salt 
of  the  acid,  water,  and  chlorine. 

Complete  the  equation : 

OC1 
Ca  +H2SO4 — >- +    + 

\, 

Chlorine  reacts  with  water  to  produce  hydrochloric  acid  and 
oxygen,  which  changes  the  coloring  matter  of  many  colored 
compounds  into  a  colorless  substance. 

(cT)  Use  of  antichlor. 

Free  chlorine  must  not  be  permitted  to  remain  in  contact 
with  the  cotton  fiber,  because  chlorine  weakens  the  strength 
of  the  fiber  by  reacting  with  it. 

Wash  the  cotton  to  remove  the  acid. 
How  can  you  determine  when  this  has  been  accomplished  f 

Put  a  little  of  the  starch  iodide  paste  on  the  cotton.  Look 
carefully  to  see  whether  a  blue  tint  is  developed.  Chlorine 
liberates  iodine  from  sodium  iodide,  and  iodine  reacts  with 
starch  to  yield  a  blue  substance. 

Complete  the  equation  : 

C12  +  Nal  — »- +      ' 


BLEACHING   OF  COTTON  165 

Soak  the  cotton  waste  in  50  cc.  of  the  antichlor,  rinse  the 
cotton  thoroughly,  and  again  use  the  starch  iodide  paste  to  test 
for  chlorine. 


Balance  the  equation  : 


Na2S2O3  +      H2O  4-      C12 — > 
H2S04  +      HC1  + 


166  LABORATORY  EXERCISES 


EXPERIMENT   60 

Four  Ways  of  Preparing  a  Salt,  Sodium  Chloride 

These  methods  are  placed  together  for  convenience.  The  exercise  should  be 
assigned  in  advance,  and  the  calculations  in  part  (c)  should  be  made  before  coming 
to  the  laboratory. 

APPARATUS.  Apparatus  for  making  chlorine,  1  set  for  each  group  of 
five  pupils.  Apparatus  similar  to  that  shown  in  Figure  18  is  conven- 
ient, and  consists  of  a  250  cc.  flask  with  2-hole  stopper  carrying  a 
thistle  tube  and  a  delivery  tube  arranged  for  use  in  the  collection  of  a 
gas  by  the  downward  displacement  of  air,  a  ring-stand  with  1  ring,  a 
clamp,  a  small  pan  of  water,  and  a  bunsen  burner.  Bottle,  8  oz.  ; 
cover  glass  ;  ring-  stand  with  one  ring  ;  bunsen  burner  ;  bottle  with 
notched  stopper  for  dropping  hydrochloric  acid  ;  two  test  tubes  ; 
funnel  ;  evaporating  dish  ;  stirring  rod  ;  deflagration  spoon  ;  gradu- 
ate, 100  cc.  ;  wire  gauze  with  asbestos  center. 

MATERIAL.  Fine  sand  ;  sodium  ;  manganese  dioxide  ;  hydrochloric 
acid,  concentrated  ;  hydrochloric  acid,  1  to  4  ;  sodium  hydroxide 
solution,  1  to  10;  solution  of  crystallized  barium  chloride,  104 
grams  of  BaCl2  •  2  H2O  per  liter  ;  solution  of  crystallized  sodium 
sulphate,  137.5  grams  of  Na2SO4  •  10H20  per  liter;  sodium  car- 
bonate, dry;  litmus  paper,  red  and  blue. 

(a)   Direct  combination. 

This  part  of  the  experiment  should  be  performed  under  a  hood. 

Collect  an  8  oz.  bottle  of  chlorine  prepared  by  any  conven- 
ient method,  for  example  that  described  in  Experiment  18. 

Half  fill  the  bowl  of  a  deflagration  spoon  with  sand.  Ask 
the  instructor  to  place  a  piece  of  clean  sodium  on  the  sand.  At 
once  take  the  sodium  to  the  hood  containing  the  bottle  of 
chlorine,  ignite  the  sodium  by  directing  a  flame  against  it,  and 
immediately  lower  the  burning  sodium  into  the  chlorine. 

What  chemical  reaction  takes  place  between  the  sodium  and  the 

chlorine?  ,  , 


FOUR    WATS   OF  PREPARING  A   SALT  167 

Why  did  it  occur  readily  (see  Experiment  $6)  ? 

.    ^ 


By  what  properties  canj/ou  identify  the^  product? 

^^^^^^t£>  • 

Name  the  product. 


(5)  Neutralization. 

In  a  porcelain  evaporating  dish,  neutralize  5  cc.  of  a  solution 
of  sodium  hydroxide  with  a  solution  of  dilute  hydrochloric 
acid.  Evaporate  the  neutral  solution  to  dryness. 

What  is  the  name  of  the  solid  obtained  ?     -fy^^/r  ^L^cL 

What  ion  does  every  water  solution  of  an  acid  contain?       ^b/ft 

A^i/          V' 

What  ion  does  every  water  solution  of  a  base  contain?     j&f  /T 

What  becomes  of  these  ions  during  the  process  of  neutralization? 
t/J  n  j-t|Af  n  if  A  j     jff~  <mA  ^-*~^ 

What  ions  are  left  in  solution  after  the  sodium  hydroxide  solution 
is  neutralized  with  hydrochloric  acid? 


What  compound  is  formed  on  evaporation  by  the  combination  of 
these  ions? 


Why  do  neutralization  reactions  tend  to  go  to  an  end? 


4& 


(c)   Double  replacement  due  to  an  insoluble  product. 

Write  the  equation  for  the  reaction  between  a  barium  chloride  solu- 
tion and  a  solution  of  sodium  sulphate. 


*  >u  - 

Why  does  the  reaction  go  to  an  end  ? 

Be.  SO 


^ri   ***  - 

168  LABORATORY  EXERCISES 

Using  the  equation 

Na2S04  •  10  H20  +  BaCl2  •  2  H20  ->  BaS04  +  2  NaCl  + 12  H20, 
and  the  table  of  atomic  weights  on  page  234)  calculate 

(a)  the  number  of  grams  of  crystallized  sodium  sulphate. 
(6)  the  number  of  grams  of  crystallized  barium  chloride,  required 
to  prepare  1  gram  of  sodium  chloride. 


The  stock  solution  of  barium  chloride  contains  104  grams 
of  crystallized  barium  chloride  per  liter.  The  stock  solution 
of  sodium  sulphate  contains  137.5  grams  of  crystallized  sodium 
sulphate  per  liter. 

Calculate  the  number  of  cubic  centimeters  of  (#)  the  stock  solu- 
tion of  barium  chloride,  (6)  the  stock  solution  of  sodium  sulphate, 
containing  the  weights  of  barium  chloride  and  sodium  sulphate 
respectively  that  you  found  would  react  to  yield  1  gram  of  sodium 
chloride. 


FOUR    WAYS  OF  PREPARING  A   SALT  169 

Why  are  these  calculations  necessary  9 


Measure  out  the  volume  of  barium  chloride  solution  re- 
quired and  pour  it  into  a  test  tube.  Measure  out  the  volume 
of  sodium  sulphate  required.  Pour  the  sodium  sulphate  solu- 
tion into  an  evaporating  dish,  heat  the  solution,  and  add  the 
barium  chloride  solution  to  it.  Allow  the  mixture  to  stand 
for  a  few  minutes  and  then  filter  it,  using  a  good  quality  of 
filter  paper.  If  the  first  portion  of  the  filtrate  is  not  clear, 
repeat  the  operation. 

What  is  the  precipitate  9 

What  salt  is  contained  in  the  filtrate? 

Obtain  the  salt  from  the  filtrate. 

How  did  you  accomplish  the   separation  of  the  two  compounds 
produced  9  ' 


fa 


6  MM,  'far? 


Double  replacement  due  to  the  volatility  of  one  of  the  products. 

Add  slowly,  with  constant  stirring,  hydrochloric  acid,  1  to  4, 
to  about  2  grams  of  sodium  carbonate,  until  all  of  the  sodium 
carbonate  has  dissolved. 
What  gas  is  generated  9 

Account  for  its  production. 

<*Jt   C^   ***M     *^+%Z*    ^tdffl,    b&'X&f* 

Why  did  the  reaction  go  to  an  end  9 

Evaporate  the  solution  to  dryness. 

What  became  of  the  excess  of  hydrochloric  acid?     &r  4* 

Why  did  the  reaction  go  to  an  end  9       \J^4<7 


170  LABORATORY  EXERCISES 

EXPERIMENT   61 

Cobalt  Nitrate  Tests 

APPARATUS.  Plaster  block,  made  by  pouring  a  thin  mixture  of  plaster 
of  Paris  and  water  into  a  form  on  a  glass  or  stone  slab  and  cutting 
the  mass  just  before  it  hardens  into  strips  of  suitable  size  ;  blowpipe  ; 
forceps ;  bunsen  burner. 

MATERIAL.  Zinc  sulphate  ;  alum  ;  magnesium  sulphate  ;  cobalt  nitrate 
solution  in  bottle  provided  with  dropper ;  unknowns. 

(#)  Put  a  little  of  some  zinc  compound,  as  zinc  sulphate,  in 
a  cavity  made  in  a  plaster  block  with  the  top  of  a  pair  of 
forceps.  Heat  it  as  hot  as  possible  at  the  end  of  a  small  blow- 
pipe flame.  Allow  the  residue  to  cool. 

Record  the  color  of  the  residue  in  a.  table  like  that  on  page  171. 

Moisten  the  residue  with  a  drop  or  two  of  cobalt  nitrate 
solution.  Again  heat  it  intensely,  and,  on  cooling,  note  the 
color  of  the  mass  that  remains  on  the  plaster  block. 

Record  in  the  table  the  color  obtained. 

(5)  Place  an  aluminum  compound,  as  alum,  in  a  fresh  cavity 
in  the  block.  Repeat  the  test  made  with  the  zinc  co'mpound, 
so  as  to  obtain  a  characteristic  coloration. 

Record  the  results  in  the  table. 

(<?)  Make  a  fresh  cavity  in  the  block,  and  place  in  it  some 
magnesium  sulphate.  Heat  the  sulphate  with  the  blowpipe 
until  it  glows  brightly.  Cool  and  moisten  the  fused  mass  with 
a  very  little  cobalt  nitrate.  Blow  very  vigorously,  and  allow 
the  mass  to  cool.  Note  carefully  the  delicate  coloration. 

Record  the  colors  obtained  in  the  table. 

(d)  Obtain  from  the  instructor  an  unknown  compound,  and 
test  it  with  the  blowpipe  and  cobalt  nitrate,  to  determine 
whether  it  is  a  compound  of  aluminum,  magnesium,  or  zinc. 


.    COBALT  NITRATE  TESTS 
What  color  was  obtained  in  the  second  heating? 
What  metal  did  the  compound  contain  f 
TABLE 


171 


COMPOUND  TAKEN 

COLOR  OK  RESIDUE  AFTER 
FIRST  HEATING 

COLOR  OF  RESIDUE  AFTER 
HEATING  WITH  COBALT 
NITRATE 

172  LABORATORY  EXERCISES 

EXPERIMENT  62 
Borax  Bead  Tests 

APPARATUS.     Mounted  platinum  wire  (or  glass  rod,  5"  long) ;  bunsen 

burner  ;  blowpipe,  if  desired  ;  triangular  file. 
MATERIAL.     Powdered    borax ;   cobalt   nitrate   or   oxide ;    manganese 

dioxide  ;  chrome  alum,  or  chromium  sulphate  ;  ferric  chloride  or  other 

iron  compound. 

(a)  Bend  the  end  of  a  platinum  wire  into  the  shape  of  a 
letter  J,  2  mm.  across  the  opening.  Heat  the  loop  red-hot 
and  dip  it  into  powdered  borax.  Heat  again  in  the  hottest 
part  of  the  flame.  The  borax  swells,  loses  its  water  of  crystal- 
lization, and  then  melts  to  a  transparent  glass. 

In  case  a  platinum  wire  is  not  available,  heat  the  end  of  a 
glass  rod  in  the  flame.  Then  dip  the  hot  end  into  powdered 
borax.  Heat  in  the  hottest  part  of  the  flame  the  borax  that 
sticks  to  the  rod,  until  the  borax  swells  up  to  an  irregular 
shaped  mass  on  the  end  of  the  rod. 

(5)  Touch  the  hot  irregular  mass  to  a  tiny  bit  of  some  cobalt 
compound,  as  cobalt  nitrate.  Heat  in  the  hot  outer  portion  of 
the  bunsen  flame  (oxidizing  flame),  until  a  clear  glassy  bead  is 
obtained.  Note  the  characteristic  color. 

Record  in  a  table  arranged  as  on  page  178. 

To  remove  the  bead  from  the  platinum  wire,  heat  it  red-hot 
and  quickly  shake  off  the  molten  bead  into  the  sink  or  waste 
jar.  Make  a  fresh  bead  and  examine  it.  If  it  is  not  colorless, 
repeat  the  operation. 

To  remove  the  bead  from  the  glass  rod,  scratch  it  with  a 
sharp  triangular  file,  and  break  it  off  as  you  would  cut  a  piece 
of  glass  tubing;  or  let  a  drop  of  water  fall  on  the  hot  rod  and 
tap  the  end  of  the  rod  on  a  table. 

(c?)  Touch  a  newly  made  bead  while  hot  to  a  bit  of  man- 


BORAX  BEAD   TESTS 


173 


ganese  dioxide.     Fuse  as  before.     Note  the  characteristic  color 
given  by  manganese  compounds. 

Record  in  the  table. 

(c?)  Using  a  chromium  compound,  e.g.  chrome  alum  or 
chromium  sulphate,  obtain  in  a  similar  manner  a  characteristic 
bead. 

Record  result  in  the  table. 

(e)  Obtain  the  color  characteristic  of  an  iron  compound  in 
the  oxidizing  flame. 

Record  result  in  the  table. 

TABLE 


COMPOUND  TAKEN  (NAME) 


FORMULA 


COLOR  OP  BEAD 


/ 


174  LABORATORY  EXERCISES 

EXPERIMENT  63 
Identification  of  Simple  Salts 

APPARATUS.     Platinum  wire ;  cobalt  glass  ;  charcoal  or  plaster  block  ; 

blowpipe  ;  test  tubes  ;  bunsen  burner. 
MATERIAL.     Borax ;  solutions  of  cobalt  nitrate,  silver  nitrate,  barium 

chloride,  and  ferrous  sulphate  ;  dilute  nitric  and  hydrochloric  acids ; 

concentrated  sulphuric  acid  ;  unknown. 

Use  a  very  small  portion  of  the  unknown  given  you  in 
making  each  test.  Always  keep  a  portion  for  verification  of 
your  results. 

Keep  a  tabulated  record  of  all  tents,  even  those  giving  negative 

results. 

(a)  Determine  the  metallic  part  of  the  substance  by  means 
of  (1)  the  flame  test  for  sodium  and  potassium,  (2)  cobalt 
nitrate,  test,  (3)  borax  bead  test. 

(6)  Then  put  a  fresh  portion  of  the  unknown  into  a  test 
tube  avid  try  to  dissolve  it  in  water,  heating  if  necessary. 
Filter  if  there  is  an  undissolved  residue. 

Divide  the  clear  liquid  into  several  portions  and  make  tests 
for  a  chloride,  a  sulphate,  and  a  nitrate. 

(0)  Now  determine  whether  the  unknown  contains  a  carbon- 
ate by  the  addition  of  an  acid  and  making  the  limewater  test  of 
the  gas  that  is  given  off. 

Finally  decide  what  you  have  found  in  the  unknown  substance, 
with  reasons  for  your  decision.  Then  take  your  note  book  to  the 
instructor. 


IDENTIFICATION  OF  SIMPLE  SALTS 

Number  of  unknown . 

TABLE 


175 


TEST 


RESULT 


The  unknown  contains 


176 


LABORATORY  EXERCISES 


EXPERIMENT   64 
Action  of  Metals  on  Salt  Solutions 

APPARATUS.     Eight  test  tubes  ;  test  tube  rack  ;  piece  of  glass. 
MATERIAL.     Four  strips  of  zinc,  10  X  1  cm.;  four  copper  strips,  10  X  1 

cm.;  iron  nails;    solutions  of   lead   acetate,  copper  sulphate,  silver 

nitrate,  mercury  nitrate,  and  zinc  nitrate. 

(#)  In  separate  test  tubes  place  solutions  of  lead  acetate, 
copper  sulphate,  silver  nitrate,  and  mercury  nitrate.     In  each 

tube  place  a  strip  of  zinc,  bend- 
ing it  over  the  lip  of  the  tube 
(Figure  49).  Let  each  tube 
stand  for  at  least  5  minutes  with- 
out disturbance. 

(5)   In  a  similar  manner,  place 
strips    of  copper  in   another   set 
of    test    tubes,    containing    lead 
acetate,    silver    nitrate,  zinc    ni- 
trate, and  mercury  nitrate. 
(#)  Remove  the  zinc  strip  that  has  been  in  the  solution  of 
mercury  nitrate.     Rinse  the  strip,  and  then  rub  it  with  the 
finger.     Bend  the  strip  sharply,  and  observe  the  broken  edge. 
What  metal  has  been  deposited  on  the  zinc? 


Figure  49. 


Remove  the  copper  strip  from  the  solution  of  mercury 
nitrate.     Rinse  the  strip,  and  rub  it  between  the  fingers. 
What  has  been  deposited  on  the  copper? 

What   does  the  color   of  the  solution  remaining  in  the  test  tube 
indicate  ? 


(e)  Remove  the  zinc  strip  from  the  silver  nitrate,  scraping 
off  the  deposit  on  it  into  the  test  tube.  Carefully  pour  off 
the  liquid  and  fill  the  test  tube  with  water.  Shake  the  tube 


ACTION   OF  METALS  ON  SALT  SOLUTIONS 


177 


and  allow  the  deposit  to  settle.     Pour  off  the  water  again. 
Gather  the  solid  together,  squeezing  it  into  a  pellet.     Lay  it  on 
something  hard  and  rub  it  with  a  piece  of  glass. 
What  metal  was  deposited  on  the  zinc? 

(/)  To  recognize  very  clearly  the  metal  that  is  deposited 
from  the  copper  sulphate  solution,  place  an  iron  nail  in  a  copper 
sulphate  solution. 
Result? 


Examine  all  the  other  strips  and  tabulate  results. 
TABLE 


METAL  STRIP 


SOLUTION 


DEPOSIT 


i/U    4A*, 

* 


^  „ 

/ 


Write  equations  for  all  cases  where  a  replacement  actually  occurs, 
but  not  for  the  others. 


178  LABORATORY  EXERCISES 

Explain  why  these  reactions  occur  (see  Experiment  28). 


Assuming  that  one  gram  of  silver  was  deposited,  what  would  have 
been  the  weight  of  copper  passing  into  the  solution? 


EQUIVALENT  OF  SILVER  179 

EXPERIMENT   65 
Equivalent  of  Silver 

APPARATUS.  Beaker  ;  balance  ;  set  of  weights  ;  wash  bottle  (Figure  50); 
glass  rod  with  rubber  tubing  on  the  end  ;  funnel ;  test  tube  ;  ring- 
stand  with  one  ring. 

MATERIAL.  Silver  nitrate  solution,  34  grams  per  liter ;  piece  of 
copper,  3x6  cm.  ;  thread  ;  filter  paper ;  ammonium  hydroxide,  1 
to  3. 

Record  weighings  in  a  table  like  that  on  page  180. 

(a)  Weigh  accurately  on  a  balance  a  piece  of  clean  bright 
copper.  Tie  a  piece  of  thread  about  it,  curve  it  slightly,  and 
suspend  it  in  a  beaker  containing  enough'  silver  nitrate  solu- 
tion to  completely  cover  it.  Allow  the  copper  to  remain  in  the 
solution  overnight. 

Write  the  equation  for  the  replacement  that  occurs. 

(I)  The  next  laboratory  period,  loosen  the  lightly  adhering 
silver  from  the  copper,  and  lift  the  strip  from  the  solution  by 
the  thread.  Every  particle  of  the  silver  must 
be  washed  from  the  copper  into  the  beaker.  It 
may  be  necessary  to  rub  the  copper  gently  with 
the  end  of  a  glass  rod  covered  with  a  bit  of 
rubber  tubing.  The  deposit  does  not  adhere 
tightly  and  is  more  easily  removed  by  gentle 
treatment  than  by  hard  rubbing. 

A  wash  bottle  (Figure  50),  by  which  a  fine 
jet  of  water  can  be  directed  against  the  copper, 
will  be  of  great  assistance  in  getting  the  silver        Figure  50. 
into  the  beaker. 

Wipe  the  copper  strip,  dry  it  at  the  ordinary  temperature, 
and  weigh  it. 

What  does  the  change  in  weight  represent? 


180  LABORATORY  EXERCISES 

(c)  While  the  copper  is  drying,  carefully  filter  the  contents 
of  the  beaker  on  a  weighed  filter  paper.1  Be  sure  that  every 
particle  of  the  silver  is  transferred  to  the  filter  paper.  The 
wash  bottle  will  be  of  great  help  in  this  operation  also. 

The  silver  must  now  be  thoroughly  washed  with  water. 
Cover  the  deposit  on  the  filter  paper  with  water  and  allow  it  to 
drain  completely  before  adding  another  portion.  Wash  in  this 
way  at  least  three  times,  or  oftener,  until  a  few  drops  of  the 
filtrate  falling  into  a  little  ammonia  water  in  a  test  tube  show 
no  coloration. 

Take  at  least  twenty-four  hours  to  dry  the  filter  unless  the 
heat  of  an  air  bath  or  a  steam  radiator  is  available,  but 
the  final  drying  must  be  done  at  the  temperature  of  the 
laboratory. 

When  dry,  weigh  the  filter  paper  and  its  contents. 

TABLE 


Original  weight  of  piece  of  copper     ........  g. 

Final  weight  of  piece  of  copper g. 

Weight  of  copper  used g. 

Weight  of  filter  paper  with  silver g. 

Weight  of  filter  paper  (obtained  from  instructor)  ...  g. 

Weight  of  silver  deposited g. 


Knowing  the  weight  of  the  metals  used,  calculate  the  number  of 
grams  of  silver  that  would  be  replaced  by  one  gram  of  copper. 

Taking  31.8  grams  of  copper  as  chemically  equivalent  to  one  gram 
of  hydrogen,  calculate  the  weight  of  silver  that  will  be  equivalent  to 
one  part  by  weight  of  hydrogen. 

1  The  weight  of  the  filter  paper  can  be  ascertained  by  weighing  the  entire 
pack,  and  then  dividing  the  weight  by  the  number  of  sheets. 


EQUIVALENT  OF  SILVER  181 

CALCULATIONS 


182  LABORATORY  EXERCISES 

Ml/" 

EXPERIMENT   66 

Tests  for  Iron  Salts 

APPARATUS.     Six  test  tubes  ;  test  tube  rack. 

MATERIAL.  Solutions  of  ferrous  sulphate  or  other  soluble  ferrous  salt 
(freshly  prepared  and  thoroughly  reduced),  ferric  chloride,  potassium 
ferrocyanide,  potassium  ferri  cyanide  (freshly  prepared). 

These  tests  involve  the  use  of  two  substances  that  are  complex 
cyanides.  Potassium  ferrocyanide,  K4Fe(CN)6,  is  a  compound 
of  potassium  cyanide,  KCN,  and  ferrous  cyanide,  Fe(CN)2. 
Potassium  ferricyanide,  K3Fe(CN)6,  is  a  compound  of  potassium 
cyanide,  KCN,  and  ferric  cyanide,  Fe(CN)3.  Note  that  the 
valence  of  iron  in  each  of  the  compounds  can  be  found  by 
subtracting  the  number  of  potassium  atoms  from  the  number  of 
cyanogen  groups,  and  that  the  name  of  each  of  the  compounds 
indicates  the  valence  of  the  iron  it  contains.  These  two  com- 
pounds ionize  according  to  the  following  equations  : 

K4Fe(CN)6  ;£  4  K+  +  Fe(CN)6- 
K3Fe(CN)6  ^±  3  K+  +  Fe(CN)6— 

In  writing  the  formulas  of  compounds  that  contain  these  com- 
plex ions  it  is  sometimes  desirable  to  use  brackets,  as  in  the 
formula  for  ferric  ferrocyanide  :  Fe4[Fe(CN)6]3. 

(a)  To  5  cc.  of  a  solution  of  ferrous  sulphate  (or  other 
ferrous  salt)  add  a  few  drops  of  potassium  ferrocyanide 
solution. 

Record  the  color  of  the  precipitate  in  the  table. 

To  5  cc.  of  a  solution  9f  ferric  chloride  (or  other  ferric  salt) 
add  a  few  drops  of  potassium  ferrocyanide. 

Record  the  color  of  the  precipitate  in  the  table. 
This  substance  is  known  as  Prussian  blue. 
Write  the  equation  for  its  formation. 


f  W     3  «<  U'   7>  5 


TESTS  FOR   IRON  SALTS 


183 


To   a   mixture  of   solutions  of  ferrous  sulphate   and  ferric 
chloride  add  a  few  drops  of  potassium  ferrocyanide  solution. 
Which  color  obscures  the  other?    Q 

£i.  ^£5£L  * 

7s  potassium  ferrocyanide  a  test  for  the  ferrous  or  for  the  ferric 


(6)  To  5  cc.  of  a  solution  of  ferrous  sulphate  (or  other  ferrous 
salt),  add  a  few  drops  of  potassium  ferricyanide. 

Record  the  color  of  the  precipitate  in  the  table.    &£,&&&&*&  < 
This  is  known  as  Turnbull's  blue. 

Write  the  equation  for  its  formation. 
0  r'  ^Lj//      PA    (     (li*)       *-V"    / 

J  r£>o  uq  UK-S  rO~  L  ^v     /    '   ^. 

To  5  cc.  of  a  solution  of  ferric  chloride  (or  other  ferric  salt), 
add  a  few  drops  of  potassium  ferricyanide.  Fill  the  test  tube 
with  water,  shake  the  contents,  and  examine  the  mixture  closely, 
to  see  whether  the  liquid  is  clear  or  a  precipitate  is  formed. 

Record  the  result  in  the  table. 

To   a  mixture  of   solutions  of  ferrous  sulphate  and  ferric 
chloride,  add  a  few  drops  of  potassium  ferricyanide. 
Is  the  precipitate  due  to  the  ferrous  or  to  the  ferric  salt? 

Is  potassium  ferricyanide  a  test  for  the  ferrous  or  for  the  ferric- 
ion? 

TABLE 


IRON  SALTS 

POTASSIUM  FEKROCYANIDE, 
K<Fe(CN)« 

POTASSIUM  FKRKICYANIDE, 
K»Fe(CN)« 

Ferrous  sulphate 
FeSO4 

Ferric  chloride 
FeCl3 

184 


LABORATORY  EXERCISES 


EXPERIMENT   67 
Action  of  a  Reducing  Agent  on  a  Ferric  Salt 

APPARATUS.    Three  test  tubes  ;  bunsen  burner  ;  test  tube  holder  ;  single- 
hole  rubber  stopper  to  fit  test  tube,  provided  with  a  short  glass  tube 

drawn  to  a  capillary. 

'    .*   ,  -...,_  ..,;'*  /'/f/ 

MATERIAL.    Solution  of  ferric  chloride;   di- 
lute hydrochloric  acid,  1  to  4 ;   steel  wool 
•  or  fine  iron  wire  ;   potassium  ferrocyanide 
solution. 

To  10  cc.  of  a  solution  of  ferric 
chloride  contained  in  a  test  tube,  add  a 
small  bundle  of  steel  wool  or  fine  iron 
wire  and  3  cc.  of  dilute  hydrochloric 
acid.  Close  the  tube  with  a  rubber 
stopper  containing  a  tube  that  ends  in 
a  capillary  (Figure  51).  Heat  the  tube 
gently. 

From  time  to  time  pour  a  very  small 
sample  of  the  contents  of  the  tube  into  a  second  test  tube  that 
contains  a  few  drops  of  potassium  ferrocyanide,  using  a  fresh 
portion  of  ferrocyanide  for  each  test. 
Results? 


Figure  51. 


What  change  is  indicated  by  these  tests? 


-.--  ^vy:-:^ 


Continue  the  boiling  until  the  tests  indicate  that  the  change 
is  complete. 

Show  by  an  equation  what  is  produced  by  the  reaction  between  the 
iron  and  the  dilute  hydrochloric  acid. 

Show  by  a  second  equation  how  one  of  these  products  reacts  with 
the  ferric  chloride. 

'  6  . 

it 


ACTION   OF  A   REDUCING  AGENT  ON  A   FERRIC  SALT     185 
What  change  occurs  in  the  valence  of  the  iron  ion  9 

&      JL 

The  terms  oxidation  and  reduction  are,  on  this  account,  some- 
times extended  to  mean  change  of  valence. 

When  used  in  this  way,  does  reduction  imply  a  raising  or  a  lower- 
ing of  valence  of  the  positive  ion  ? 

"frv-t-k  •  '-A 


186  LABORATORY  EXERCISES 

EXPERIMENT   68 

Action  of  an  Oxidizing  Agent  on  a  Ferrous  Salt 

APPARATUS.     Three  test  tubes  ;  bunsen  burner. 

MATERIAL.     Solution  of  ferrous  sulphate  ;  dilute  sulphuric  acid,  1  to  6  ; 

hydrogen  peroxide  ;  concentrated  nitric  acid  ;   solutions  of  potassium 

ferrocyanide  and  potassium  ferricyanide. 

To  5  cc.  of  a  solution  of  ferrous  sulphate,  add  1  cc.  of  dilute 
sulphuric  acid  and  2  cc.  of  hydrogen  peroxide.  Test  small 
samples  of  the  resulting  solution  for  ferrous  ions  and  for  ferric 
ions. 


Results? 


Complete  the  equation  : 
FeS04  +  H2S04  +  H202 


What  change  occurs  in  the  valence  of  the  iron  ions  ? 
Why  is  this  change  sometimes  spoken  of  as  oxidation  ? 

Try  the  effect  of  nitric  acid  on  a  mixture  of  ferrous  sulphate 
and  dilute  sulphuric  acid.     Boil  the  contents  of  the  tube,  and 
test  for  both  ferrous  and  ferric  ions. 
Results? 

t~f  I  '     •^"••'•^     •        .     ^;.,O 

1~     *'      ^ 

Complete  the  equation : 

•  FeS04  +    -H2S04+      HN03 


Wlienused  to  indicate  a  change  of  this  kind,  does  oxidation  imply 
a  raiding  or  a  lowering  of  the  valence  of  the  positive  ion  ? 


IRON  SALTS  IN  PHOTOGRAPHY -BLUE  PRINTS       187 


EXPERIMENT   69 


Iron  Salts  in  Photography 


Blue  Prints 

test  tubes ;  grad- 


APPARATUS.     Two  enameled  pans,  shallow,  8  X  10" 
uate,  100  cc. 

MATERIAL.  Solution  of  ammonium  ferric  citrate  (green  scales),  100  g. 
in  1  liter;  ferric  chloride  solution,  4  g.  in  100  cc. ;  potassium  fern- 
cyanide  solution,  100  g.  in  1  liter;  oxalic  acid  solution,  50  g.  in 
1  liter  ;  paper,  unglazed,  of  good  quality,  cut  into  sheets  3"  X  4". 

(a)  Prepare  two  pieces  of  sensitive  paper.  This  should  be 
done  in  a  darkened  room,  closet,  or  cupboard.-  Holding  the 
paper  by  a  corner,  draw  it 
lightly  across  the  surface  of  a 
solution  of  ammonium  ferric 
citrate  contained  in  a  shallow  pan 
(Figure  52).  Avoid  getting 
the  back  of  the  paper  wet  with 
the  solution,  and  make  sure 
that  the  face  is  completely  and 
evenly  moistened.  Hang  the 
paper  to  dry  in  a  dark  place. 

(5)  In  a  darkened  room  or 
cupboard,  mix  in  a  test  tube 
3  cc.  of  ferric  chloride  with  3  cc. 
of  oxalic  acid  solution.  Divide 

this  mixture  into  two  parts.  Keep  one  part  in  the  dark,  while 
exposing  the  other  to  the  direct  rays  of  the  sun  for  several 
minutes.  To  each  of  the  tubes  then  add  3  cc.  of  a  solution  of 
potassium  ferricyanide. 

In  which  tube  has  a  ferrous  salt  been  produced  f 


Complete  the  equation: 


HC1  +      CO, 


188  LABORATORY  EXERCISES 

This  is  an  example  of  a  chemical  action  produced  by  light. 
Which  of  the  substances  may  be  regarded  as  having  been  reduced? 

Which  may  be  regarded  as  the  reducing  agent? 

(<?)  Ammonium  ferric  citrate  makes  an  excellent  substance 
for  preparing  blue  print  paper,  because  it  contains  within  itself 
both  the  iron  salt  and  the  reducing  agent. 

When  the  paper  prepared  with  ammonium  ferric  citrate  at 
the  beginning  of  the  period  is  thoroughly  dry,  arrange  it  for 
exposure  to  sunlight  so  that  an  opaque  object,  such  as  a  key,  or 
a  stencil  cut  in  heavy  paper,  will  keep  the  light  from  striking 
part  of  the  paper.  The  exposure  should  last  three  to  ten 
minutes  according  to  the  strength  of  the  light.  At  the  end  of 
this  time,  examine  the  paper  quickly,  and  then  immerse  it,  face 
down,  in  a  pan  containing  a  solution  of  potassium  ferricyanide. 
Was  any  change  apparent  before  the  paper  was  put  into  the 

solution  ? 

After  it  was  put  into  the  solution  ? 

Complete  the  equation : 
FeCl,  +  K3Fe(CN)6  — ^ + 


Wash  the  paper  thoroughly  in  running  water,  dry  it,  and 
paste  it  in  the  place  provided  on  the  next  page. 

What  purpose  does  potassium  ferricyanide  serve  in  this  operation  ? 


What  common  photographic  term  might  be  applied  to  the  potassium 
ferricyanide  ? 

Why  is  it  necessary  to  wash  the  paper  thoroughly  ? 


IRON   SALTS  IN  PHOTOGRAPHY— BLUE  PRINTS        189 
What  photographic  term  can  be  applied  to  this  part  of  the  operation? 

SAMPLE  PRINT 


190  LABORATORY  EXERCISES 

C-  •         1  Q^ 
EXPERIMENT    70 

Silver  Salts  in  Photography 

APPARATUS.  Three  test  tubes,  which  must  be  clean  and  entirely  free 
from  grease  ;  small  graduate. 

MATERIAL.  Solutions  of  silver  nitrate  (17  grams  per  liter),  potassium 
bromide  (36  grams  per  liter),  hypo  (25  per  cent  solution)  ;  developer  as 
follows:  1600  cc.  water,  10  grams  hydrochinone,  20  grams  sodium 
sulphite  (dry)  ;  1  gram  potassium  bromide,  1  gram  citric  acid, 
20  grams  sodium  carbonate  (dry)  ;  or  the  ordinary  developing  powders 
may  be  used,  diluting  according  to  directions  for  tank  use ;  dark 
paper. 

Protect  the  materials  from  the  light,  by  wrapping  a  dark 
paper  about  the  test  tubes.  Do  not  warm  with  the  hands. 
All  materials  must  be  pure  and  the  test  tubes  must  be  clean. 

In  each  part,  (#),  (&),  and  (c),  suspended  silver  bromide 
is  prepared  by  adding  to  a  test  tube  one  fourth  full  of  water, 
not  more  than  1  cc.  of  potassium  bromide  solution  and  an  exactly 
equal  amount  (1  cc.)  of  silver  nitrate  solution;  mix  well,  but 
do  not  shake  hard.  (If  shaken  hard,  the  bromide  will  become 
lumpy.) 

(a)  Expose  silver  bromide  to  the  light  for  a  few  minutes, 
shaking  it  to  expose  all  parts  equally.  (The  bromide  may 
change  color,  if  impure.) 

To  the  exposed  bromide,  add  about  5  cc.  of  the  developing 
solution.     Allow  the  action  to  continue  for  two  minutes. 
Result? 


Then  add  about  10  cc.  of  hypo  solution  (fixer),  and  shake 
well. 

Result? 


SILVER   SALTS  IN  PHOTOGRAPHY 


191 


(J)  To  the  suspended  silver  bromide  (well  protected  from 
the  light)  add  5  cc.  of  developer.     Keep  in  the  dark  for  two 
minutes. 
Remit? 


Then  add  about  10  cc.  of  the  fixer. 
Result? 

(<?)  To  the  suspended  silver  bromide  add  about  10  cc.  of  the 
fixer. 

Remit? 

TABLE 


SILVER  BROMIDE  EXPOSED 
TO  LIGHT 

SILVER  BROMIDE  NOT 
EXPOSED  TO  LIGHT 

Action  of  developer 
Action  of  fixer 

The  developer  is  a  reducing  agent  capable  of  continuing,  but  not 
initiating,  the  reduction  of  a  silver  salt. 

Under  what  conditions  is  an  insoluble  residue  (silver)  obtained? 


"Hypo"  is  the  last  solution  used  in  the  preparation   of  a 
negative. 

What  is  its  action? 


192  LABORATORY  EXERCISES 

EXPERIMENT    71 
Aluminum  Hydroxide 

APPARATUS.     Hydrometer  jar,  or  cylindrical  graduate,  250  cc.  ;  three 

test  tubes  ;  glass  stirring  rod,  15". 
MATERIAL.     Aluminum  sulphate,  20  g.  to  the  liter;   limewater ;    fine 

clay;  ammonium  hydroxide  solution,    1   to    10;    logwood  solution; 

alizarine  mixed  with  water. 

(#)   Preparation. 

To  one  sixth  of  a  test  tube  of  a  dilute  solution  of  aluminum 
sulphate,  A12(SO4)3,  add  twice  as  great  a  volume  of  lirnewater. 
Result? 

What  is  the  appearance  of  this  precipitate  of  aluminum  hydroxide  ? 
Write  the  equation  for  the  precipitation. 


(5)   As  a  coagulum. 

Add  water  to  a  cylindrical  jar  until  it  is  about  two  thirds 
full.  Render  the  water  turbid  by  stirring  in  a  little  fine  clay. 
Then  pour  in  one  third  of  a  test  tube  of  aluminum  sulphate 
solution  and  mix  it  with  the  turbid  water  by  thorough  stirring. 

To  this  mixture,  add  slowly,  without  stirring,  two  thirds  of  a 
test  tube  of  limewater.  Allow  the  water  to  stand. 

Note  what  is  happening  from  time  to  time. 
Result? 

What  precipitate  was  formed  in  the  turbid  ivater? 

How  are  the  suspended  particles  of  clay  removed  so  as  to  leave  the 
water  clear? 


ALUMINUM  HYDROXIDE  193 

(tf)   Formation  of  lakes. 

To  one  sixth  of  a  test  tube  of  logwood  solution,  add  ammonium 
hydroxide.  Note  that  no  precipitate  is  formed,  although  the 
logwood  changes  somewhat  in  color. 

To  a  solution  of  aluminum  sulphate  in  another  test  tube,  add 
some  ammonium  hydroxide. 
What  is  the  precipitate? 

Add  some  logwood  solution  to  the  test  tube  containing  the 
precipitate.    Shake  the  test  tube  and  allow  the  contents  to  settle. 
What  does  the  color  of  the  liquid  in  the  test  tube  show  about  the 
amount  of  logwood  in  solution? 

Compare  the  color  of  the  precipitate  with  the  color  of  logwood  and 
with  the  color  of  aluminum  hydroxide. 


Such  a  combination  of  a  dye  with  aluminum  hydroxide  or 
other  suitable  compound,  is  commonly  called  a  "lake." 

Formerly  aluminum  hydroxide  was  extensively  used  in  dyeing 
cloth.  Its  gelatinous  nature  enables  it  to  adhere  to  the  fibers 
of  the  cloth.  It  also  adheres  to  the  dye.  Thus  it  acts  as  a 
binder  between  the  cloth  and  the  dye.  A  substance  that  has 
this  characteristic  is  said  to  be  a  mordant. 

State  how  you  would  dye  a  piece  of  white  cotton  cloth  by  using  the 

same  three  solutions  employed  to  make  the  logwood  lake. 


Using   aluminum   sulphate   solution,   ammonium   hydroxide 
solution,  and  alizarine,  make  an  alizarine  lake. 

How   does  the   alizarine   lake  differ  in  color  from  the  original 
alizarine  and  from  the  aluminum  hydroxide? 


194 


LABORATORY  EXERCISES 


EXPERIMENT   72 

Substantive,  Salt,  or  Direct  Colors  for  Cotton 

APPARATUS.  Five  agateware  cups  or  stewpans,  1  pt. ;  two  ring- stands 
with  ring  ;  two  bunsen  burners  ;  balance  sensitive  to  0. 1  g.  and  weights  ; 
yard-stick  ;  shears  ;  funnel,  3J" ;  three  stirring  rods  ;  two  test  tubes, 
6";  graduate,  100  cc. 

MATERIAL.  Sodium  carbonate  solution,  2  g.  Na2CO3  per  liter ;  white 
cotton  cloth  (cheesecloth)  ;  white  woolen  yarn ;  saturated  solution 
of  plaster  of  Paris  ;  saturated  solution  of  salt ;  stock  solution  of  Congo 
red,  5  g.  to  the  liter ;  stock  solution  of  sodium  chloride,  50  g.  to  the 
liter  ;  Castile  soap  ;  filter  paper. 

(a)  Weigh  a  piece  of  unbleached  cotton  cloth  (cheesecloth) 
and  also  determine  the  number  of  square  inches  it  contains. 
Calculate  the  number  of  square  inches  weighing  approximately 
10  g.  and  cut  the  cloth  into  strips  containing  this  number  of 

square  inches. 

(5)  To  aid  in  obtaining  an 
even  color,  the  material  to  be 
dyed  should  be  clean  and  satu- 
rated with  water  before  being 
placed  in  the  dye  bath.  The 
treatment  preparatory  to  dyeing 
varies  with  the  kind  of  goods, 
the  impurities  adhering  to  the 
fiber,  the  shade  to  be  obtained, 
and  the  nature  of  the  dye. 

Pour  into  a  pint  agateware 
cup  (Figure  53)  200  to  300  cc. 
of  the  solution  of  sodium  car- 


Figure  53. 


bonate,  add  two  strips  of  cloth,  and  bring  the  liquid  to  a  gentle 
boil.  Continue  to  boil  the  cloth  gently  until  it  is  required 
for  use  in  part  (/). 

Take  a  skein  of  white  woolen  yarn  weighing  approximately 


SUBSTANTIVE,   SALT,  OR  DIRECT  COLORS   FOR   COTTON      195 

5  g.  and  boil  it  in  suds  made  by  dissolving  Castile  soap  in  warm 
water.  Let  gentle  boiling  continue  until  the  yarn  is  required 
for  use  in  part  (/). 

(<?)  Pour  5  cc.  of  a  saturated  solution  of  plaster  of  Paris  into 
a  test  tube  and  add  a  few  drops  of  a  0.5%  solution  of  Congo 
red.     Mix  the  liquids  thoroughly  and  then  filter. 
Describe  the  substance  left  on  the  filter. 


Congo  red  is  the  sodium  salt  of  an  acid.  The  calcium  and 
magnesium  salts  of  this  acid  are  insoluble  and,  therefore,  are 
formed  when  Congo  red  is  added  to  the  hard  water.  A  similar 
action  takes  place  with  most  of  the  substantive  colors. 

Why  should  a  hard  ivater  be  softened  before  being  used  in  a  dye 

bath? 


To  5  cc.  of  a  nearly  saturated  solution  of  salt  in  a 
test  tube, 'add  a  few  drops  of  a  0.5%  solution  of  Congo  red. 
Thoroughly  mix  the  contents  of  the  tube  and  allow  it  to  stand 
for  a  few  minutes,  then  filter. 

What  do  you  observe  concerning  the  color  of  the  filtrate  ? 


The  Congo  red,  being  less  soluble  in  the  salt  solution  than  in 
pure  water,  was  precipitated.  This  process  is  technically 
termed  "salting  out." 

(e)  In  preparing  a  dye  bath,  the  quantity  of  dye  used  de- 
pends upon  the  weight  of  the  material  to  be  colored,  the  color 
used,  and  the  shade  to  be  obtained.  In  three  agateware 
vessels  prepare  the  following  baths  : 

Bath  ft  1.  Dissolve  in  300  cc.  of  soft  water  a  quantity  of 
Congo  red  equal  in  weight  to  2  per  cent  of  the  weight  of  one  of 
the  pieces  of  cotton  cloth.  This  weight  is  calculated  as  follows  : 


196  LABORATORY  EXERCISES 

1  cc.  of  the  stock  solution  of  Congo  red  contains  0.005  g.  of 
Congo  red.  Each  piece  of  cloth  weighs  10  g.  Two  per  cent 
of  10  g.  is  0.2  g.  Your  bath  should  contain  0.2  g.  of  Congo 

0  2 
red,  or      '      =  40  cc.  of  the  stock  solution. 

Bath  #  2.  To  300  cc.  of  water,  add  40  cc.  of  the  stock  solu- 
tion of  Congo  red  and  sodium  chloride  equal  in  weight  to 
20  per  cent  of  a  piece  of  cloth.  1  cc.  of  the  stock  solution  of 
salt  contains  0.05  g.  of  sodium  chloride. 

How  many  cubic  centimeters  of  the  stock  solution  of  sodium  chloride 

should  be  used? 


Bath  $  8.  To  300  cc.  of  water,  add  Congo  red  equal  in 
weight  to  2  %  of  a  skein  of  wool  (5  g.)  and  salt  equal  to  20  % 
of  the  weight  of  the  skein. 

Calculate  and  record  the  volume  of  the  stock  solutions  required. 


(f)  Remove  the  cotton  cloth  and  the  woolen  yarn  from  the 
baths  used  in  part  (6).  Thoroughly  rinse  the  cotton  and  the 
wool  in  soft  water  and  then  distribute  the  material  as  follows : 

Place  a  strip  of  cotton  cloth  in  Bath  f  1. 

Place  a  strip  of  cotton  cloth  in  Bath  $  2. 

Place  a  skein  of  woolen  yarn  in  Bath  f  3. 

Heat  the  baths  to  boiling  and  continue  gentle  boiling  for 
fifteen  minutes.  During  the  boiling,  frequently  move  the  goods 
in  the  baths  so  as  to  make  sure  that  the  dye  comes  in  contact 
with  every  part  of  the  material. 

(#)  Remove  the  goods  from  the  baths,  wash  thoroughly  in 
water,  and  then  dry.  Examine  the  liquid  remaining  in  the 
agateware  vessels. 


SUBSTANTIVE,  SALT,  OR  DIRECT  COLORS  FOR   COTTON     197 

Did  the  cotton  or  the  wool  extract  the  more  color  from  the  bath  ? 

Compare  the  color  of  the  cloth  dyed  in  the  bath  containing  no 
salt  with  that  dyed  in  the  bath  containing  salt. 

• 

In  which  case  was  the  more  dye  deposited  on  the  goods? 
After  referring  to  part  (d)  account  for  this  fact. 


Place  a  piece  of  white  cloth  and  a  piece  of  colored  cotton 
cloth  in  a  dish  half  filled  with  water  and  boil  for  a  few  minutes. 
Result? 

Colors  that  behave  in  this  way  are  said  to  "  bleed  " ;  that  is, 
they  are  not  fast  in  washing. 

Direct  colors  vary  greatly  in  their  fastness  to  washing,  their 
fastness  to  light,  and  their  comparative  affinity  for  cotton  and 
wool. 

Attach  each  piece  of  cloth  as  an  exhibit  in  the  place  provided 
for  it. 

SAMPLES  DYED  IN  CONGO  RED 


COTTON,  BATH 
No.    1 

COTTON,  BATH 
No.  2 

WOOL,  BATH 
No.  3 

SAMPLES, 
PART  (h) 

198  LABORATORY  EXERCISES 

EXPERIMENT    73 
Acid  Colors 

APPARATUS.  Two  agateware  vessels,  1  pt. ;  ring-stand  with  ring ;  bunsen 
burner;  two  glass  stirring  rods;  thermometer;  pipette,  lOcc. ;  bal- 
ance with  weights  ;  graduate,  100  cc. 

MATERIAL.  Two  pieces  of  cotton  cloth  (cheesecloth)  weighing  5  g. 
each  ;  two  skeins  white  woolen  yarn  weighing  5  g.  each  ;  stock  solution 
of  Biebrich  scarlet,  tartrazine,  or  acid  blue  containing  5  g.  to  the  liter 
(dissolve  the  color  in  hot  water)  ;  stock  solution  of  Glauber's  salt 
(cryst.  sodium  sulphate)  containing  50  g.  to  the  liter ;  stock* solution 
of  sulphuric  acid  made  by  dissolving  55  cc.  of  sulphuric  acid  (sp.  gr. 
1.84)  in  water  and  diluting  to  1  liter  ;  picric  acid  ;  sodium  carbonate  ; 
Castile  soap. 

(a)  Prepare  5  g.  samples  of  cotton  cloth  and  of  woolen  yarn 
for  the  dye  bath  by  boiling  the  cotton  in  a  dilute  solution  of 
sodium  carbonate  and  the  wool  in  a  soap  solution  as  directed  in 
Experiment  72. 

(6)  Dissolve  0.1  g.  of  picric  acid  in  300  cc.  of  water  in  an 
agateware  vessel.  Warm  to  60°  C.  and  then  add  a  sample  of 
cotton  cloth  and  one  of  woolen  yarn.  Raise  the  temperature  of 
the  bath  to  near  its  boiling  point.  Remove  the  samples  and 
wash  them  thoroughly. 
Results? 


(<?)  The  acid  colors  are  nearly  all  salts  of  color  acids  from 
which  the  color  acid  is  liberated,  during  the  process  of  dyeing, 
by  the  addition  of  another  acid,  generally  sulphuric,  to  the 
bath.  More  sulphuric  acid  than  the  amount  necessary  to 
liberate  the  color  acid  is  added  to  the  bath,  because  the  excess 
of  sulphuric  acid  acts  on  the  wool  and  causes  it  to  have  a 
greater  tendency  to  combine  with  the  dye.  The  addition  of 
sodium  sulphate  to  the  bath  generally  improves  the  evenness  of 


ACID   COLORS  199 

the  deposition  of  color  on  the  fiber ;  its  chief  action  probably  is 
to  retard  the  rate  of  liberation  of  the  color  acid. 

Prepare  a  dye  bath  by  adding  to  300  cc.  of  water,  2  cc.  of  the 
stock  solution  of  sulphuric  acid,  10  cc.  of  the  stock  solution 
of  Glauber's  salt,  and  10  cc.  of  the  stock  solution  of  color. 

How  many  grams  does  the  bath  contain  (a)  of  sulphuric  acid? 

(b)  of  Glauber's  salt?     (c)  of  color? 


The  bath  contains  the  usual  quantities  used  for  dyeing  5  g.  of 
wool. 

What  per  cent  of  the  weight  of  the  wool  is  (a)  the  sulphuric  acid  ? 
(b)  the  Glauber's  salt?     (c)  the  color  that  is  used? 


Warm  the  bath  to  60°  C.,  and  add  5  g.  of  woolen  yarn. 
Raise  the  temperature  of  the  bath  to  near  its  boiling  point  and 
continue  that  temperature  for  ten  minutes,  meanwhile  working 
the  goods  in  the  bath.  Remove  the  wool  from  the  bath  and 
wash  it  thoroughly.  Into  another  bath,  prepared  in  a  similar 
manner,  put  5  g.  of  cotton  cloth  and  heat  it  as  you  did  the 
woolen  yarn. 

To  which  kind  of  material,  cotton  or  wool,  does  the  dye  adhere  more 

firmly? 


200 


LABOEATORY  EXERCISES 


Acid  colors  are  used  chiefly  in  dyeing  woolen  and  silk  goods. 
As  a  class,  they  are  fast  to  light,  but  not  to  washing,  and  con- 
sequently are  suitable  for  dyeing  goods  not  intended  to  be 
washed.  A  few  of  them  are  fast  to  washing,  and  some  of  them 
dye  wool  but  not  silk. 

Attach  a  sample  of  each  of  the  pieces  of  cloth  in  the  place 
provided  for  it. 

» 
SAMPLES 


COTTON,  PICRIC 
ACID 


WOOL,  PICRIC 
ACID 


COTTON, 
PART  (c) 


WOOL, 
PART  (c) 


BASIC  COLORS  201 

EXPERIMENT    74 
Basic  Colors 

APPARATUS.  Two  beakers,  200  cc. ;  two  agateware  vessels,  1  pt. ;  ring- 
stand  with  ring;  bunsen  burner;  three  glass  stirring  rods;  100  cc. 
graduate. 

MATERIAL.  Cheesecloth,  10  g.  pieces;  blue  litmus  paper;  standard 
tannic  acid  solution,  10  g.  per  liter  ;  standard  solution  of  tartar  emetic, 
10  g.  tartar  emetic  per  liter;  standard  solution  of  malachite  green, 
5  g.  malachite  green  per  liter ;  standard  solution  of  Fuchsine,  5  g. 
Fuchsine  per  liter  ;  acetic  acid  ;  soft  or  distilled  water. 

Basic  colors  are  direct  colors  for  wool  and  silk,  but  do  not 
adhere  to  cotton.  Cotton,  however,  can  be  treated  with  sub- 
stances, called  mordants,  that  cling  to  the  fiber  and  also  to  the 
color.  By  the  use  of  mordants  the  color  is  held  to  the  cotton 
fiber. 

(a)  Add  20  cc.  of  the  standard  solution  of  tannic  acid  to 
100  cc.  of  water  in  a  200  cc.  beaker  and  heat  nearly  to  boiling. 
If  the  water  used  is  hard,  add,  previous  to  the  dissolving  of  the 
tannic  acid,  sufficient  acetic  acid  to  give  a  slightly  acid  reaction 
with  litmus. 

Put  10  g.  of  cheesecloth  in  the  hot  solution  of  tannic  acid 
and  allow  it  to  remain  for  at  least  two  hours,  allowing  the  solu- 
tion of  tannic  acid  to  cool  meanwhile.  If  more  convenient, 
allow  the  cheesecloth  to  remain  in  the  tannic  acid  bath  until 
the  next  laboratory  period. 

(5)  Pour  100  cc.  of  water  into  a  beaker  and  add  10  cc. 
of  the  standard  solution  of  tartar  emetic.  Remove  the 
cloth  that  has  been  in  the  tannic  acid  solution  a  sufficient 
length  of  time,  squeeze  it,  and  put  it  into  the  cold  tartar  emetic 
bath. 

The  tartar  emetic  combines  with  the  tannic  acid  to  form 
an  insoluble  salt  that  adheres  to  the  cotton  fiber. 

(<?)  Prepare  in  the  agateware  vessels  two  duplicate  dye 
baths.  In  each  case,  add  to  200  cc.  of  water  sufficient  acetic 


202  LABORATORY  EXERCISES 

acid  to  make  the  bath  slightly  acid,  and  then  add  40  cc.  of  the 
standard  solution  of  malachite  green. 

The  acetic  acid  serves  the  double  purpose  of  correcting  any 
hardness  that  may  be  in  the  water,  and  of  preventing  a  too 
rapid  dyeing  of  the  goods  that  might  result  in  unevenness 
of  shade. 

In  one  dye  bath,  place  10  g.  of  cheesecloth  that  has  not  been 
mordanted. 

Take  a  piece  of  cheesecloth  from  the  tartar  emetic  and  wash 
it  thoroughly  in  soft  water.  Then  put  the  cheesecloth  into  the 
dye  bath  not  in  use. 

Slowly  heat  the  two  dye  baths  to  about  60°  C.  and  dye  the 
pieces  of  cloth  for  ten  minutes  or  more,  meanwhile  moving  them 
in  the  bath  so  as  to  expose  all  parts  to  the  action  of  the  dye. 

Remove  the  pieces  of  cloth  from  the  dye  baths  and  wash 
them  thoroughly  with  water,  being  careful  to  use  different 
portions  of  water  for  each  piece  of  cloth. 

To  which  piece  of  cloth  does  the  dye  adhere  the  more  firmly? 


Divide  into  two  equal  parts  the  piece  of  cloth  that  has  been 
mordanted  and  then  dyed.  Dip  one  of  them  in  a  dye  bath 
made  by  adding  4  cc.  of  a  standard  solution  of  Fuchsine  to 
300  cc.  of  water  that  was  slightly  acidified  by  acetic  acid.  Re- 
move the  cloth  as  soon  as  it  becomes  thoroughly  wet  by  the 
Fuchsine  solution,  wash,  and  then  note  the  effect  of  the  red  on 
the  brilliancy  of  the  green. 
Result? 


Attach  a  sample  of  each  of  the  pieces  of  cloth  in  the  space 
provided  for  it. 


BASIC  COLORS                                              203 

SAMPLES 

UNMORDANTED 
MALACHITE  GREEN 

MORDANTED 
MALACHITE  GREEN 

MALACHITE  GREEN 

AND   FUCHSINE 

. 

.*?$< 

204  LABORATORY  EXERCISES 

EXPERIMENT   75 

Double  Salts 

APPARATUS.     100  cc.  flask;  250  cc.  beaker;   two  beakers,  100  cc.  ; 

stirring  rod  ;  balance  and  weights  ;  funnel ;  tripod  ;  bunsen   burner ; 

wire  gauge  with  asbestos  center  ;  graduate. 
MATERIAL.     The  material  for  the  preparation  of  each  salt  will  be  found 

accompanying  the  directions  for  making  the  salt. 

(#)   Preparation  of  ferrous  ammonium  sulphate, 

FeSO4(NH4)2SO4  .  6  H2O. 

MATERIAL.  Filter  paper ;  iron  wire  or  nails ;  ammonium  hydroxide  ; 
concentrated  sulphuric  acid  ;  sulphuric  acid,  1:10;  red  and  blue  lit- 
mus papers. 

Take  50  cc.  of  dilute  sulphuric  acid  in  a  flask  and  dissolve  in 
it  clean  iron  wire  as  long  as  hydrogen  is  given  off. 

Write  the  equation  for  the  formation  of  ferrous  sulphate,  FeS04. 

While  waiting  for  the  wire  to  dissolve,  take  another  50  cc.  of 
dilute  sulphuric  acid  in  a  beaker  and  neutralize  with  ammonium 
hydroxide  solution. 

What  salt  is  formed  9 

Write  the  equation. 

Filter  the  ferrous  sulphate  solution  into  the  solution  of 
ammonium  sulphate. 

Evaporate  the  mixed  solution  to  one  third  its  volume.  Add 
a  few  drops  of  the  concentrated  sulphuric  acid  and  set  the 
solution  aside  to  crystallize. 

Pour  off  the  liquid  into  the  bottle  designated  by  the  in- 
structor. Empty  the  crystals  of  the  ferrous  ammonium  sul- 
phate on  a  filter  paper  in  a  funnel.  When  the  crystals  have 


DOUBLE  SALTS  205 

drained,  dry  them  between  sheets  of  filter  paper.     They  can  be 
used  for  making  the  test  for  nitrates. 

Write   the  equation  for   the   formation   of  ferrous  ammonium 
sulphate. 


(5)   Preparation  of  potassium  alum,  KA1(SO4)2  •  12  H2O. 

MATERIAL.     Filter  paper ;  potassium  sulphate  ;  aluminum  sulphate. 

Write  the  equation  for  the  preparation  of  i>otassium  alum  from 
2)otassium  sulphate  and  aluminum  sulphate. 

Weigh  out  15  grams  of  crystallized  aluminum  sulphate, 
A12(S04)3.18H20. 

Calculate  from  the  equation  how  many  grams  of  potassium  sul- 
phate are  needed. 


Weigh  out  the  calculated  amount  of  potassium  sulphate  and 
dissolve  in  40  cc.  of  hot  water. 

In  another  beaker  dissolve  the  aluminum  sulphate  in  40  cc.  of 
hot  water. 

Mix  the  two  solutions  and  set  the  mixture  aside  to  crystal- 
lize in  a  place  where  the  beaker  will  not  be  disturbed. 


206  LABORATORY  EXERCISES 

0)   Ammonium  alum,  (NH4)Al(SO4)a  •  12  H2O. 

MATERIAL.  Crystallized  aluminum  sulphate ;  ammonium  hydroxide, 
sp.  gr.  0.90  ;  sulphuric  acid,  1:10;  filter  paper ;  red  and  blue  litmus 
papers. 

Weigh  out  15  grams  of  aluminum  sulphate,  and  dissolve  it  in 
40  cc.  of  water. 

Add  4.5  cc.  of  ammonium  hydroxide  solution  to  15  cc.  of 
water,  neutralize  it  with  dilute  sulphuric  acid,  and  then  dilute 
it  to  about  40  cc. 

Mix  the  two  solutions,  filter  the  mixture  if  it  is  not  clear,  and 
evaporate  the  solution  to  half  the  bulk. 

Set  the  solution  aside  to  crystallize. 

Describe  the  color  and  general  form  of  the  crystals. 


Write  the  equations  for  the  reactions  taking  place. 


Ferric  ammonium  alum,  (NH4)Fe(SO4)2  •  12  H2O. 

MATERIAL.  Filter  paper ;  ammonium  hydroxide,  iron  wire  or  nails ; 
sulphuric  acid,  1:10;  concentrated  nitric  acid  ;  red  and  blue  litmus 
papers. 

Prepare  a  solution  of  ferrous  sulphate  as  in  part  (a). 

Prepare  a  solution  of  ammonium  sulphate  as  in  part  (a). 

To  the  filtered  solution  of  ferrous  sulphate  in  a  beaker,  add 
25  cc.  of  the  sulphuric  acid,  and  1  cc.  of  concentrated  nitric  acid. 
Boil  as  long  as  nitric  oxide  is  evolved. 

Into  what  gas  is  nitric  oxide  converted  on  coming  in  contact  with  air? 

The  iron  is  now  in  solution  as  ferric  sulphate,  Fe2(SO4)3. 
Write  the  equation  for  the  reaction. 


DOUBLE  SALTS  207 

Add  the  solution  of  ammonium  sulphate  to  the  solution  of 
ferric  sulphate,  evaporate  until  the  bulk  is  reduced  to  one  half. 
Set  the  beaker  aside  to  cool  slowly  until  the  contents  crystallize. 
Describe  the  color  and  general  form  of  the  crystals. 


The  crystals  may  be  dried  between  blotters ;  they  must  be 
preserved  in  well-stoppered  bottles. 

Write  the  equation  for  the  reaction  between  the  sulphate  of  iron 
and  the  ammonium  sulphate. 


(«)   Rochelle  salt,  NaK(C4H4O6)  -  4  H2O. 

MATERIAL.     Cream  of  tartar  ;  bicarbonate  of  soda  ;  fitter  paper. 

Weigh  out  14  g.  of  acid  potassium  tartrate  (cream  of  tartar), 
KH(C4H4O6).  Mix  it  with  15  cc.  of  water. 

Does  it  completely  dissolve  in  this  quantity  of  water? 

Weigh  out  6  g.  of  sodium  bicarbonate,  NaHCO3,  and  mix  it 
with  15  cc.  of  water. 

Does  it  completely  dissolve  in  this  quantity  of  water? 

While  stirring,  slowly  pour  the  sodium  bicarbonate  solution 
into  that  of  the  tartrate,  and  pour  back  from  beaker  to  beaker 
until  action  ceases. 

What  gas  is  evolved  ? 

Is  all  the  solid  dissolved  ? 


208  LABORATOBY  EXERCISES 

If  the  liquid  is  not  clear,  filter  it,  and  evaporate  it  to  half 
bulk  and  set  it  aside  to  crystallize.  Better  crystals  may  be 
obtained  by  setting  it  aside  to  evaporate  without  heating,  but 
do  not  let  it  evaporate  to  dryness.  Pour  off  the  mother  liquor 
and  dry  the  crystals  between  blotters  or  filter  paper. 

Write  the  equation  for  the  reaction  between  sodium  bicarbonate  and 
cream  of  tartar. 


(/)   Rochelle  salt,  NaK(C4H4O6)  .  4  H2O. 

ATERIAL.      Tartaric  acid  ;    sodium    hyd 
droxide,  1  :  10;  phenolphthalein  paper. 


MATERIAL.      Tartaric  acid ;    sodium    hydroxide,  1  :  10;  potassium  hy- 


Dissolve  5  g.  of  tartaric  acid  in  10  cc.  of  water.     Exactly 
/  neutralize  it  with  sodium  hydroxide. 

Dissolve  5  g.  of  tartaric   acid  in  10  cc.   of  water.     Exactly 
;'/  neutralize  it  with  potassium  hydroxide. 

Mix  the  two  solutions  and  evaporate  to  one  half  the  bulk  or, 
to  get  good  crystals,  set  it  aside  to  evaporate  slowly  to  one 
fourth  the  bulk.  Pour  off  the  mother  liquor  and  dry  the 
crystals  between  blotters  or  filter  paper. 

Write  the  equation  for  the  reaction  between   sodium  hydroxide 
and  tartaric  acid,  H2(C4H406). 


Write  the  equation  for  the  reaction  between  potassium  hydroxide 
and  tartaric  acid. 


Write  the  equation  for  the  reaction  which  resulted  in  the  formation 
of  the  Rochelle  salt. 


DOUBLE  SALTS  209 

($r)   Ammonium  sodium  tartrate. 

MATERIAL.     Tartaric  acid  ;  ammonium  hydroxide  ;  sodium  hydroxide; 
phenolphthalein  paper. 

Proceed  as  above,  but  use  ammonium  hydroxide  instead  of 
potassium  hydroxide.     Ammonium  sodium   tartrate   does  not 
crystallize  as  well  as  Rochelle  salt. 
Write  equation  as  in  part  (/). 


210  LABORATORY  EXERCISES 

(^   "V ,  \  Ot~ 
EXPERIMENT   76 

Qualitative  Separation  of  Lead,  Silver,  and  Mercury 

APPARATUS.     Test  tubes  ;  test  tube  rack  ;  funnel ;  bunsen  burner. 

MATERIAL.  Hydrochloric  acid  concentrated  and  dilute ;  nitric  acid 
concentrated  and  dilute  ;  ammonium  hydroxide  1  to  3  ;  solutions 
of  lead,  silver,  and  mercurous  nitrates  ;  potassium  chromate  solution  ; 
copper  strip  ;  filter  paper  ;  unknown  solutions. 

(a)  In  one  test  tube  take  10  cc.  of  a  solution  of  lead  nitrate  ; 
and  in  another,  10  cc.  of  a  solution  of  silver  nitrate.  To  both 
test  tubes  add  dilute  hydrochloric  acid  till  the  reaction  is  com- 
plete. 

,    ,   ,  / *      >     \ 

Results?  ,.  -i  , 


Write  the  equations. 

(  4   "it      :    ^ 


'    £ 
i 

Allow  the  precipitates  to  settle  and  then  pour  off  the  super- 
natant liquid  from  each  of  the  two  test  tubes.  Add  to  the 
precipitates  in  the  test  tubes  enough  cold  water  to  nearly  fill 
the  tubes,  and  shake  the  contents.  Again  let  the  precipitates 
settle  and  then  pour  off  the  supernatant  liquids. 

What  compound  has  been  removed  by  washing  the  precipitate  and 

then  pouring  off  the  supernatant  liquid  ? 

Try  the  effect  of  hot  water  on  the  precipitate  of  lead  chloride. 
Result? 

Divide  the  precipitate  of  silver  chloride  between  two  test 
tubes.  With  one  part  try  the  effect  of  hot  water ;  with  the 
other,  the  effect  of  ammonium  hydroxide. 


SEPARATION  OF  LEAD,   SILVER,  AND  MERCURY      211 
Results?     £-     M.HL,.&'-&-4&  t£i^U~i*** 


Cxt^**W     *^~  A 

<W^  0kA^fW*±. 


To  10  cc.  of  a  solution  of  mercurous  nitrate,  HgNO3,  add 
dilute  hydrochloric  acid  till  the  action  is  complete.      . 

Result?  '-tAA*^**'  /MA^tJw&jjL  41W 


Write  the  equation. 


Wash  the  precipitate  with  cold  water  and  divide  it  between 
two  test  tubes.  Find  out  whether  hot  water  dissolves  the 
mercurous  chloride. 

Result?  uM^/ 

What  effect  does  ammonium  hydroxide  have  upon  the  mercurous 
chloride?   Jk^^   tfrtfa  j  &   x^A^i  . 

(<?)  In  the  same  test  tube  take  5  cc.  each  of  solutions  of  silver, 
lead,  and  mercurous  nitrates.  Add  dilute  hydrochloric  acid 
till  precipitation  is  complete. 

Of  what  does  the  precipitate  consist  ? 

Filter.  Wash  the  precipitate  on  the  filter  paper  with  a  very 
little  cold  water.  Next  wash  the  precipitate  thoroughly  with 
hot  water,  keeping  the  washings. 

Which  one  of  the  chlorides  was  dissolved  by  the  hot  ivater? 

•it  • 

To  confirm  this,  add  to  the  hot  filtrate  a  solution  of  potassium 
chromate,  K2CrO4.  This  chromate  gives  an  insoluble  and 
characteristic  compound  of  the  metal  whose  chloride  is  soluble 
in  hot  water. 

Write  the  equation  for  this  confirmatory  test. 

> 


212  LABORATORY  EXERCISES 

Give  name,  formula,  and  color  of  the  characteristic  compound 
formed. 


Wash   the   precipitate  remaining  on  the   filter   paper  with 
ammonium  hydroxide,  keeping  the  washings. 
Which  chloride  gives  the  color? 

What  chloride  is  contained  in  the  ammonium  hydroxide  filtrate  ? 


Prove  the  presence  of  this  chloride  by  adding  a  slight  excess 
of  nitric  acid. 

Name  the  precipitate  and   state   the  characteristic  properties  by 
which  you  recognize  it. 


To  dissolve  the  precipitate  still  remaining  on  the  filter  paper, 
add  a  little  aqua  regia  (9  drops  concentrated  hydrochloric  acid 
to  3  drops  concentrated  nitric  acid).  Dilute  with  water  the 
solution  thus  obtained,  and  put  into  it  a  bright  strip  of  copper. 
After  several  minutes,  remove  the  strip,  and  wash  and  rub  it. 
Result?  £ 


Explain  why  this  dissolving  in  aqua  regia  and  the  addition  of  a 
copper  strip  is  a  confirmatory  test. 


(c?)  Obtain  from  the  instructor  an  unknown  solution.  Using" 
the  methods  in  (V),  analyze  the  solution  for  lead,  silver,  and 
mercury. 


SEPARATION  OF  LEAD,   SILVER,   AND  MERCURY        213 

Record  all  the  steps,  even  those  giving  negative  results. 


Underline  the  metal  found  in  your  unknoivn. 
lead  mercury  silver 


214  LABORATORY  EXERCISES 

EXPERIMENT    77 

Chromium  Compounds 

APPARATUS.    Two  beakers,  250  cc.  ;  two  test  tubes;  graduate;  balance 

and  weights  ;  bunsen  burner. 
MATERIAL.      Potassium    dichromate  ;    potassium    hydroxide  ;    sodium 

peroxide  ;    chromium    sulphate    or   chrome   alum  ;    alcohol  ;    dilute 

nitric  acid  ;  concentrated  sulphuric  acid. 

(a)  Pulverize  10  grams  of  potassium  dichromate  and  dissolve 
it  in  50  cc.  of  water.  The  color  of  the  solution  is  characteristic 
of  dichromate  ions. 

(5)  Dissolve  10  grams  of  potassium  hydroxide  in  100  cc.  of 
water. 

((?)  Slowly  add,  with  constant  stirring,  the  solution  prepared 
in  (£>)  to  that  prepared  in  (#)  until  the  resulting  liquid  is  of  a 
pure  yellow  color.  The  color  is  characteristic  of  chromate  ions. 

Complete  the  equation  :/ 

K2Cr207  +  2  KOHV1-^  2  K2CrO4+  _ 

Any  strong  base  would  produce  this  change. 

K—  O—  Cr 

The  structural  formula  for  potassium  dichromate  is  \0 

K—  O—  Cr^zO 
%0 

K-° 

The  structural  formula  for  potassium  chromate  is 


What  is  the  valence  of  chromium  in  each  case  ? 

(cT)  Add  a  dilute  solution  of  nitric  acid  to  the  solution  ob- 
tained  in    (<?)   until  the  color  of   the  liquid  shows  that  the 
chromate  ions  have  been  changed  to  dichromate  ions. 
Write  the  chemical  equation  representing  the  change. 


CHROMIUM  COMPOUNDS  215 

Why  might  a  solution  of  any  strong  add  be  used  in  place  of  the 
nitric  acid? 

(e)  Drop  by  drop,  pour  1  cc.  of  concentrated  sulphuric  acid 
into  5  cc.  of  water. 

Dissolve  1  grain  of  powdered  potassium  dichromate  in  10  cc. 
of  water  and  then  add  1  cc.  of  alcohol. 

Pour  the  first  solution  into  the  second.  Warm  the  mixture 
gently.  The  green  color  is  due  to  chromic  ions,  from  the 
compound  chromic  sulphate. 


The  formula  for  chromic  sulphate  is 

r>\ 

4 

When  a  dichromate  is  changed  into  a  chromic  salt,  is  the  change 
one  of  oxidation  or  of  reduction  ?          rt      / 

Why? 


(/)  Add  sodium  peroxide,  a  little  at  a  time,  to  1  gram  of 
chromium  sulphate  or  chrome  alum  dissolved  in  25  cc.  of  water, 
until  the  yellow  color  characteristic  of  chromate  ions  has  been 
produced. 

What  element  is  liberated  when  sodium  peroxide  is  added  to  water? 

What  base  is  formed  ? 


change  takes  place  when  a  chromic  salt  is  oxidized  in  the 
presence  of  a  base? 


216  LABORATORY  EXERCISES 

P  V        ' 
EXPERIMENT   78 

Fermentation 

APPARATUS.      Acid  bottle,  capacity  about  2^  liters ;  two  wide-mouth 
bottles,  capacity  about  500  cc. ;  stoppers  and  tubes  shown  in  Figure  54 
test  tube;  boiling  flask,  250  cc. ;   U-tube,  6" ;  battery  jar,  5"  high 
stoppers  and  tubes  shown  in  Figure  55  ;  thermometer ;  watch  glass 
beaker,  100  cc. ;  ring-stand  with  1  ring  and  a  small  clamp;   bunsen 
burner ;  wire  gauze  with  asbestos  center. 

MATERIAL.     Molasses;   two  yeast  cakes;    limewater ;    iodine;    quick- 
lime ;  sodium  hydroxide  solution ;  candle  or  splinter. 

(a)   Fermentation. 

Arrange  apparatus  as  shown  in  Figure  54.  One  set  of  ap- 
paratus will  furnish  sufficient  fermented  liquid  for  ten  pupils  to 

use  in  part  (6).  Pour  1  vol- 

=»M=^  ume  Of  molasses  dissolved  in 

4m  6  volumes  of  water  into  the 

acid  bottle.  Break  two  yeast 
cakes  into  small  fragments  and 
stir  them  into  a  little  luke- 
warm water,  so  as  to  form  a 
thin  paste.  Pour  the  paste 
into  the  bottle  containing  the 
solution  of  molasses,  then  shake 
the  bottle  so  as  to  distribute 
the  yeast  through  the  molasses. 


y 


Figure  54. 


After  replacing  the  stopper  in  the  acid  bottle,  remove  the 
stopper  from  the  wide-mouth  bottle  connected  with  the  acid 
bottle,  and  fill  the  bottle  with  water.  Replace  the  stopper. 
Some  of  the  water  will  be  forced  into  the  third  bottle,  but  no 
siphoning  can  take  place  since  air  cannot  enter  the  acid  bottle. 

Allow  the  apparatus  and  contents  to  remain  in  a  warm 
place  for  several  days  (about  a  week).  From  time  to  time, 
examine  the  contents  of  the  bottles. 


FERMENTATION  217 

What  change  do  you  notice  in  the  color  of  the  liquid  in  the  acid 
tip.  9 


bottle? 


What  has  happened  to  the  water  in  the  wide-mouth  bottles?. 


While  the  action  is  in  progress,  remove  the  third  bottle  for  a 
moment  and  replace  it  with  a  test  tube  containing  a  little  lime- 
water  so  arranged  that  the  end  of  the  delivery  tube  will  be  in 
the  limewater. 

Account  for  the  result. 


After  the  action  has  been  going  on  for  several  days,  remove  the 

stopper  from  the  bottle  filled  with  gas  and  lower  into  it  a  lighted 

candle,  or  burning  splinter. 

Results? 


What  is  the  name  of  the  gas? 


(5)   Fractional  distillation. 

Arrange  apparatus  as  shown 
in  Figure  55. 

Siphon  off  enough  of  the  fer- 
mented liquid  to  half  fill  a  dis- 
tilling flask  and  clamp  the  flask 
in  place.  Insert  the  thermome- 
ter so  that  its  bulb  is  in  the  neck 
of  the  flask  just  below  the  de- 
livery tube. 


Figure  55. 


218  LABORATORY  EXERCISES 

After  connecting  the  condensing  tube  to  the  flask,  bring  the 
liquid  in  the  flask  to  a  gentle  boil,  then  regulate  the  tempera- 
ture very  carefully,  in  order  to  prevent  froth  from  being  formed 
and  passing  over  into  the  distillation  tube. 

Why  should  the  water  in  the  battery  jar  be  changed  occasionally 

or  lumps  of  ice  be  put  in  the  water  ? 


At  ivhat  temperature  does  the  liquid  commence  to  distil  over? 

When  the  temperature  has  reached  85°,  take  away  the  flame. 
Remove  the  U-tube  from  the  water,  wipe  it  dry  on  the  outside, 
and  pour  enough  of  its  contents  into  a  watch  glass  to  make  a 
circle  as  big  as  a  quarter.  Hold  a  bunsen  flame  to  the  watch 
glass  for  a  moment. 
What  happens? 

What  is  shown  to  be  present  by  this  test? 

After  the  action  is  over,  is  any  liquid  left  in  the  watch  glass? 

Stop  the  distillation  at  99°  C. 

At  the  close  of  the  distillation  try  to  ignite  a  few  drops  of 
the  distillate. 
Result? 

Throw  away  the  liquid  in  the  flask. 

Place  in  the  distilling   flask  a  number  of  small  lumps  of 
quicklime.     Pour  the  first  distillate  back  into  the   flask  and 
redistil  it,  noticing  the  temperature  of  the  vapor. 
Why  is  the  lime  used  ? 

Identify  the  second  distillate  (a)  by  its  odor,  (5)  by  bringing 
a  lighted  match  to  a  small  portion  in  a  watch  glass,  and  (<?)  by 
applying  the  iodoform  test  to  another  portion.  To  make  the 


FERMENTATION  219 

iodoform  test,  add  to  the  liquid  to  be  tested  a  little  sodium 
hydroxide  solution,  and  then  iodine,  a  crystal  at  a  time,  and 
warm.  Stop  the  addition  of  the  iodine  before  a  permanent 
brown  color  is  obtained.  The  iodoform  will  separate  as  a 
yellow  precipitate  and  can  be  recognized  by  its  odor. 

During  the  fermentation,  the  cane  sugar  in  the  molasses  was 
converted  into  a  mixture  of  two  simpler  sugars,  dextrose  and 
levulose : 

(VI^O,,  4-  H20  -+  C6H1206  +  C6H1206 

cane  sugar         water  dextrose  levulose 

This  change  was  brought  about  by  a  ferment  (invertase) 
produced  during  the  growth  of  the  yeast  plant.  Then  another 
ferment  (zymase),  also  from  the  yeast,  caused  the  change  of  the 
simpler  sugars  into  ethyl  alcohol,  C2H5OH,  and  the  gaseous 
product  you  tested. 

Complete  the  equation  for  this  change: 


Ethyl  alcohol  boils  at  78°  C. 

Hoiu  do  you  explain   the   rise   in  the  boiling  point  during  the 
distillation? 


220  LABORATORY  EXERCISES 

EXPERIMENT    79 
Preparation  of  Ethereal  Salts  (Esters) 

APPARATUS.     Bunsen  burner ;  three  test  tubes ;    notched  cork  to  fit 

test  tube. 
MATERIAL.     Sulphuric  acid,  concentrated  ;   sodium  acetate ;   salicylic 

acid  ;  ethyl  alcohol,  95  per  cent ;  amyl  alcohol ;  methyl  alcohol. 

(a)   Ethyl  acetate. 

Dissolve  enough  sodium  acetate  to  fill  the  curved  bottom  of 
a  test  tube  in  a  very  little  water,  and  then  add  a  few  drops  of  con- 
centrated sulphuric  acid.  Acetic  acid  is  produced,  H(C2H3O2). 

Complete  the  equation : 

NaC2H3O2  +  H2SO4  -+  Na2SO4  +_ 

To  the  contents  of  the  test  tube  add  a  few  drops  of  ethyl 
alcohol.  Warm  the  tube  gently,  and  note  a  distinctive  odor, 
different  from  that  of  alcohol.  This  is  due  to  ethyl  acetate, 

CTT  p    TT    f\ 

2H5  *  ^2H3U2" 

Write  the  equation  for  its  formation. 

(5)   Amyl  acetate. 

Put  1  drop  of  amyl  alcohol,  C5HUOH,  into  a  test  tube,  add 
two  drops  of  concentrated  sulphuric  acid,  and  then  add  a  small 
pinch  of  sodium  acetate.  Warm  the  test  tube  gently.  Remove 
the  tube  from  the  flame,  and,  from  a  test  tube  with  a  notched 
cork,  let  water  run,  a  drop  at  a  time,  down  the  side  of  the  tube, 
until  about  3  cc.  have  been  added.  Again  warm  the  test  tube, 
shaking  it  as  you  do  so.  Note  the  distinctive  odor.  Amyl 
acetate  has  been  formed. 

In  what  paint  have  you  noted  this  odor? 

Of  what  fruit  does  it  remind  you  ? 


PREPARATION  OF  ETHEREAL   SALTS  221 

(<?)  Methyl  salicylate. 

Put  a  small  pinch  of  salicylic  acid  into  a  test  tube.     Add  a 
drop  of  methyl  alcohol,  and  about  20  drops  of  concentrated 
sulphuric  acid.     Warm  the  mixture  very  gently,  shaking  the 
tube  as  you  do  so.     Note  the  odor  produced. 
Of  what  familiar  substance  does  it  remind  you? 


General  questions. 
What  are  the  products  of  the  reaction  between  a  base  and  an  acid  ? 

What  radical  is  common  to  bases  and  alcohols? 

Show  the  similarity  between  an  ester  and  an  inorganic  salt. 


The  formation  of  esters  is  known  as  esterification.     This  is 
easily  reversed.     The  reverse  action  is  known  as  mponification, 
What  must  take  place  in  order  that  a  reaction  may  go  to  an  end  ? 


Hoiv  does  the  presence,  of  concentrated  sulphuric  acid  aid  in  the 
formation  of  esters? 


222  LABORATOBY  EXERCISES 

EXPERIMENT  80 
Soap  Making 

APPARATUS.  Bunsen  burner ;  ring- stand  ;  teaspoon  ;  evaporating  dish ; 
graduate,  25  cc. ;  stirring  rod. 

MATERIAL.  Beef  suet  (rendered  by  heating  it  in  an  evaporating  dish 
until  the  fat  is  melted,  and  then  pouring  the  fat  off  the  connective 
tissue),  or  lard ;  33  per  cent  solution  of  sodium  hydroxide. 

Place  in  an  evaporating  dish  2  level  teaspoonfuls  of  "  ren- 
dered" beef  fat,  or  lard.  Heat  the  dish  with  a  small  flame 
until  the  fat  is  melted.  Then  add  3  cc.  of  a  33  per  cent  solution 
of  sodium  hydroxide.  Warm  the  dish  very  gently  with  a  small 
flame,  stirring  the  contents  constantly.  Continue  the  heating 
until  there  is  a  soapy  mass  in  the  dish.  Then  allow  the  dish  to 
cool.  The  residue  left  in  the  dish  is  soap. 

Beef  fat  is  mainly  glyceryl  stearate,  C3H5(C18H35O2)3. 
Stearic  acid  has  the  formula  H(C18H35O2). 

Write  the  equation  for  the  reaction  between  the  glyceryl  stearate 

and  the  sodium  hydroxide,  producing  sodium  stearate  (a  soap)  and 

glycerine,  C3H5(OH)3. 

tfi/f.lk^kO/  fa  ' '  #  -> 

Organic  fats  and  oils  are  esters  of  the  alcohol  glycerine  and 
fatty  acids. 

How  are  such  fats  and  oils  converted  into  soap? 


What  alcohol  is  a  by-product  of  soap  making  f 
What  became  of  it  in  the  case  of  the  soap  just  made? 


STARCH  223 

V2  x:  *t  1 

EXPERIMENT  81 
Starch 

APPARATUS.  Beaker,  150  cc. ;  three  test  tubes;  glass  stirring  rod; 
funnel ;  porcelain  evaporating  dish ;  sand  bath ;  ring-stand  with  large 
and  small  rings ;  wire  gauze  with  asbestos  center ;  bunsen  burner. 

MATERIAL.  Starch ;  potassium  iodide  solution  of  iodine ;  glucose ; 
Fehling  solution ;  hydrochloric  acid. 

(a)   Starch  heated  with  water. 

To  one  sixth  of  a  test  tube  of  water  add  a  pinch  of  starch  and 
shake  the  tube. 

Does  the  uncooked  starch  dissolve  9 


Boil  the  mixture  in  the  test  tube  until  a  gelatinous  mass  has 
been  formed.  Pour  the  mass  into  a  beaker  of  water  and  stir 
thoroughly. 

Does  the  boiled  starch  dissolve? 


When  starch  is  heated  with  water,  the  cellulose  envelope 
inclosing  each  starch  granule  bursts,  and  a  gelatinous  mass  is 
formed.  On  longer  heating  some  of  the  starch  passes  into 
solution. 

Half  fill  a  test  tube  from  the  beaker  containing  the  starch  solu- 
tion and  keep  the  test  tube  for  part 


(6)   Test  for  starch. 

Add  a  drop  of  iodine  solution  to  the  contents  of  the  beaker. 
Result? 


224 


LABORATORY  EXERCISES 


(c)   Conversion  to  dextrine . 

Support  an  evaporating  dish  in  the  small  ring  of  a  ring-stand. 
Place  one  third  of  a  test-tubeful  of  starch  in  the  dish,  having  it 
well  above  the  small  flame  of  abunsen  burner 
(Figure  56).  The  starch  should  be  heated 
just  hot  enough  to  turn  it  barely  yellow,  but 
not  hot  enough  to  char  it.  The  temperature 
of  conversion  from  starch  to  dextrine  is  be- 
tween 200°  and  250°  C. 

Continue  the  heating  for  fifteen  minutes, 
stirring  meanwhile  with  a  glass  rod ;    then 
allow  the  dish  to  cool.     Add  a  little  water 
^^  ^^^       to  the  mass  in  the  dish,  and  stir  the  mixture. 
Rub  some  of  the  mass  between  the  fingers. 
What  characteristic  has  it? 


Figure  56. 

This  is  due  to  the  fact  that  some  of  the  starch  has  been  con- 
verted into  dextrine. 

Why  is  dextrine  used  in  making  mucilage  and  other  adhesives? 


Pour  a  few  drops  of  the  liquid  in  the  evaporating  dish  into  a 
test  tube  two  thirds  filled  with  water,  and  shake  the  test  tube. 
Then  add  a  drop  of  iodine  solution.  The  violet  to  red  color 
produced  is  characteristic  of  dextrine. 


Test  for  glucose. 

Dissolve  a  little  glucose  in  10  cc.  of  water.     Heat  in  a  second 
test  tube  10  cc.  of  Fehling's  solution  to  the  boiling  point.     To 
this  hot  liquid  add  a  little  of  the  glucose  solution. 
Result? 


STARCH  225 

To  some  of  the  starch  solution  kept  from  part  (a),  add  10  cc. 
of  the  hot  Fehling's  solution. 
Result? 


(e)   Conversion  of  starch  to  glucose. 

Put  a  little  starch  into  a  third  of  a  test  tube  of  water  and 
then  add  three  or  four  drops  of  hydrochloric  acid.  Boil  the 
mixture  for  ten  minutes. 

Test  the  resulting  liquid  with  Fehling's  solution. 
Result? 

What  change  has  occurred? 


226  LABORATORY  EXERCISES 

EXPERIMENT   82 

Food  Constituents.    Part  I 

Fats.    Protein 

APPARATUS.  Test  tubes  ;  bunsen  burner  ;  ring- stand  with  one  large  and 
one  very  small  ring  ;  two  porcelain  evaporating  dishes  ;  beaker,  150  cc. 

MATERIAL.  Benzol ;  filter  paper  ;  Geis's  biuret  reagent,  made  by  add- 
ing 3  per  cent  copper  sulphate  solution  to  10  per  cent  potassium 
hydroxide  solution  a  drop  at  a  time,  until  a  faint  but  perceptible  blue 
color  is  imparted  to  the  resulting  solution  ;  foods  for  testing,  such  as  fat 
meat,  flour,  milk,  nuts,  sugar,  peas,  etc. 

Test  several  foods  as  directed  below,  and  fill  in  the  tabular 
form. 

(a)  Test  for  oil  or  fat. 

Divide  as  finely  as  possible  the  sample  to  be  tested.  Use 
enough  to  fill  a  test  tube  to  the  depth  of  one  half  to  three 
fourths  of  an  inch.  Add  benzol  to  cover  the  solid  to  the  depth 
of  one  half  inch. 

Caution !    Benzol  is  inflammable. 

Warm  the  contents  gently  by  standing  the  test  tube  in  a 
beaker  of  hot  water.  Allow  the  test  tube  to  stand  for  five 
minutes,  with  occasional  shaking  and  warming. 

Fold  a  filter  paper  as  for  a  funnel.  Suspend  it  in  a  small 
ring  in  the  ring-stand.  Pour  a  few  drops  of  the  liquid  from 
the  test  tube  into  the  point  of  the  filter  paper,  and  allow  the 
benzol  to  evaporate  completely.  If  the  food  contains  oil  or  fat, 
more  or  less  of  a  line  of  grease  will  be  left  around  the  stained 
spot  on  the  paper.  This  can  be  more  easily  seen  if  the  paper 
is  held  to  the  light ;  the  grease  spot  then  appears  lighter  than 
the  rest  of  the  paper. 

Why  was  benzol  used? 


FATS.     PBOTEIN  227 

Why  was  the  sample  of  food  divided  as  finely  as  possible? 


(b)  Test  for  protein. 

Use  the  food  either  as  a  solution  or  in  as  finely  divided  state 
as  possible.  Put  it  into  an  evaporating  dish,  and  add  5  cc.  of 
Geis's  biuret  reagent.  Put  the  same  quantity  of  the  reagent 
into  a  second  evaporating  dish  for  comparison  in  detecting  a 
change  of  color.  If  the  food  contains  protein  matter,  the  solu- 
tion in  the  first  dish  will  acquire  a  pink  or  violet  color.  The 
change  will  be  readily  seen  if  the  two  dishes  are  compared. 
Test  several  foods  and  record  your  results  in  the  table. 


Which  of  the  foods  contained  no  protein  ? 


TABLE 


FOOD  TESTED 


FAT 
PRESENT  OR  ABSENT  ? 


PROTEIN 

PRESENT  OR  ABSENT  ? 


228  LABORATORY  EXERCISES 

EXPERIMENT   83 

Food  Constituents.    Part  II 

Carbohydrates 

APPARATUS.     Test  tubes  ;  bunsen  burner. 

MATERIAL.  Starch  ;  glucose  ;  cane  sugar ;  fruit ;  potato ;  flour ;  meat ; 
beets ;  potassium  iodide  solution  of  iodine  ;  Fehling's  solution  (pur- 
chase as  two  solutions  and  mix  just  before  using)  ;  hydrochloric  acid 
Molisch's  reagent  (15  per  cent  solution  of  a-naphthol  in  alcohol); 
concentrated  sulphuric  acid. 

(a)   Test  for  carbohydrates.     (Molischtest.) 

To  5  cc.  of  a  solution  obtained  by  boiling  the  ground  food 
with  water  for  several  minutes,  add  2  drops  of  a  solution  of  a- 
naphthol  (15  per  cent  solution  in  alcohol).  Hold  the  tube  con- 
taining this  mixture  in  an  inclined  position,  and  add  slowly 
3  cc.  of  concentrated  sulphuric  acid  in  such  a  manner  that  it 
slides  down  the  side  of  the  tube  and  makes  a  separate  layer 
below  the  mixture  already  present  in  the  tube.  A  purple  ring 
will  form  between  the  two  layers  if  the  original  solution  con- 
tained any  carbohydrate. 
Result? 


(5)   Test  for  starch. 

To  a  pinch  of  starch  add  5  cc.  of  water  and  boil  the  mixture 
in  a  test  tube  till  a  gelatinous  mass  has  been  formed.     Dilute 
this  by  nearly  filling   the  tube   with  water.     Add  a  drop  of 
iodine  solution. 
Result? 


CARBOHYDRATES  229 

(c)   Test  for  glucose. 

Dissolve  a  little  glucose  in  10  cc.  of  water.    Heat  in  a  second 
test  tube  10  cc.  of  Fehling's  solution  to  the  boiling  point.     To 
this  hot  liquid  add  a  little  of  the  solution  of  glucose. 
Result? 


(c?)  Formation  of  glucose  from  starch  and  cane  sugar. 

To  about  1  gram  of  the  starch  add  10  ec.  of  water  and  3  or  4 
drops  of  hydrochloric  acid.  Boil  the  mixture  for  ten  minutes. 
Test  the  resulting  solution  for  glucose. 


In  a  similar  way,  boil  cane  sugar  solution  with  hydrochloric 
acid  and  test  the  product  for  glucose. 
Result? 


Under  what  circumstances  can  Fehling's  solution  be  used  as  a  test 
for  cane  sugar? 


(e)   Test  of  samples. 

Test  the  samples  of  food  given  you,  first  for  carbohydrates  in 
general,  and  then  for  starch  and  glucose.  If  a  food  contains 
neither  of  these,  test  it  for  cane  sugar.  Use  the  food  in  a  finely 
divided  state,  and  boil  about  1  gram  of  it  with  10  cc.  of  water 
for  five  minutes  before  making  the  test. 

Record  your  results  in  the  table  on  page  230. 
Why  can  not  the  test  for  cane  sugar  be  used  in  the  presence  of 
starch? 


230 


LABORATORY  EXERCISES 
TABLE 


FOOD  TESTED 


STARCH 
PRESENT  OB  ABSENT  ? 


GLUCOSE  (OR  CANE  SUGAR) 
PRESENT  OR  ABSENT? 


CONSTITUENTS  OF  MILK  231 

EXPERIMENT  84 
Constituents  of  Milk 

APPARATUS.  Graduate,  100  cc. ;  beakers,  100  cc.,  250  cc.,  500  cc. ; 
watch  glass  to  cover  250  cc.  beaker ;  funnel ;  glass  stirring  rod  ;  porcelain 
crucible,  #  0 ;  pipe-stem  triangle ;  wire  gauze  with  asbestos  center ;  ring- 
stand  with  two  rings  ;  bunsen  burner  ;  test  tube  ;  two  evaporating  dishes. 

MATERIAL.  Sample  of  sweet  milk;,  acetic  acid,  10  cc.  glacial  acetic 
acid  in  740  cc.  of  water  ;  sodium  hydroxide  solution,  4  grams  of  NaOH 
per  liter ;  piece  of  blotting  paper  a  little  smaller  in  diameter  than  the 
watch  glass ;  filter  paper  to  fit  funnel ;  carbon  tetrachloride ;  Geis's 
biuret  reagent ;  Fehling's  solution  ;  milk  sugar ;  distilled  water. 

(0)   Casein. 

Pour  25  cc.  of  milk  into  a  500  cc.  beaker  and  add  175  cc.  of 
distilled  water.  Now  add,  a  drop  at  a  time  with  constant 
stirring,  40  cc.  of  the  solution  of  acetic  acid.  Allow  the 
mixture  to  stand  for  about  20  minutes,  meanwhile  proceeding 
with  part  (6).  Then  filter  the  milk.  Save  the  filtrate  for  use 
in  part  (c). 

Why  does  milk  curdle  when  it  enters  the  stomach? 


Put  the  paper  and  contents  into  a  beaker  of  water  and  rinse 
the   precipitate   from   the   paper.     The   precipitate   is   casein. 
Test  this  for  protein  by  the  method  given  in  Experiment  82. 
Result? 


Allow  the  casein  to  settle,  then  pour  off  the  liquid  and  add  to 
the  casein  100  cc.  of  the  sodium  hydroxide  solution.     If  the 
casein  does  not  dissolve,  add  a  little  more  of  the  alkali. 
How  could  casein  be  reprecipitated  from  this  solution? 


232  LABORATORY  EXERCISES 

(6)   Fat. 

Half  fill  a  250  cc.  beaker  with  water.  Set  it  on  a  piece  of 
wire  gauze  placed  on  the  ring  of  a  ring-stand,  and  heat  the 
water.  As  soon  as  the  water  commences  to  boil,  lower  the 
flame  so  it  will  furnish  only  enough  heat  to  keep  the  water 
boiling  gently.  While  waiting  for  the  water  to  boil,  wet  the 
piece  of  blotting  paper  with  milk  by  pouring  a  thoroughly 
mixed  sample  down  a  stirring  rod  so  that  it  will  drop  on  the 
paper  in  such  a  manner  as  to  distribute  the  milk  evenly  over 
the  surface  of  the  paper.  Put  the  paper  wet  with  milk  011  the 
watch  glass,  set  the  glass  on  the  beaker  of  boiling  water,  and 
allow  it  to  remain  until  the  milk  has  evaporated  to  dryness. 

Remove  the  watch  glass  containing  the  paper  and  allow  it  to 
cool.  When  the  glass  is  cold,  pour  into  it  sufficient  carbon 
tetrachloride  to  cover  the  paper.  Work  the  paper  in  the  liquid 
by  means  of  a  stirring  rod  for  two  or  three  minutes,  then 
remove  the  paper  arid  evaporate  the  carbon  tetrachloride  over 
steam. 

What  remains  on  the  ivatch  glass  ? 

(c)   Lactalbumen. 

Heat  the  nitrate  obtained  in  part  (a)  to  boiling  and  continue 
the  boiling  until  a  clear  fluid  can  be  obtained  by  filtration. 
Save  this  filtrate  for  use  in  part  (cT).     The  residue  is  lactal- 
bumen.     Determine  whether  it  is  a  protein. 
Result? 

Casein  does  not  coagulate  when  milk  is  boiled. 

What  is  the  scum  that  appears  on  the  surface  of  boiling  milk? 


Sugar. 

Fill  one  third  of  a  test  tube  with  the  filtrate  obtained  in  part 
),  add  sufficient  Fehling's  solution  to  have  the  tube  half  full 


CONSTITUENTS   OF  MILK  233 

of  the  mixture,  and  heat  the  contents  of  the  tube  to  boiling. 
Lactose,  milk   sugar,  reduces   Fehling's  solution  in  a  manner 
similar  to  glucose.     See  Experiment  83. 
Examine  a  sample  of  milk  sugar. 

How  does  its  siveetness  compare  with  that  of  sugar? 


(e)  Ash. 

Evaporate  5  cc.  of  milk  to  dryriess  in  a  porcelain  crucible 
placed  on  a  pipe-stem  triangle  supported  on  the  rim  of  a  beaker 
containing  boiling  water.  Dry  the  crucible,  then  gradually 
raise  the  temperature  to  the  full  capacity  of  your  bunsen  burner. 
Continue  the  heat  until  the  carbon  has  been  completely  burned 
and  only  a  white  ash  remains. 

Would  milk  sugar  leave  an  ash  ? 


APPENDIX 


APPENDIX 


I.     PHYSICAL    CONSTANTS 
OF   THE   IMPORTANT   ELEMENTS 

Approximate  Weights  Should  Be  Used  in  All  Calculations,  Except  Those  of 

Equivalents 


ELEMENT 

SYMBOL 

ATOMIC  WEIGHTS 

VALENCE 

SPECIFIC  GRAVITY 

MELTING 
POINT 

BOIUNO 
POINT 

Approx- 
imate 

Exact 
O=16 

Water  =1 

Air  =  1 

°C. 

°C. 

Aluminum 

Al        27 

27.1 

III 

2.7 

657 

2200 

Antimony 

Sb 

120 

120.2 

III  V 

6.6 

630 

1600 

Argon 

A 

40 

39.88 

1.38 

-  188 

-186 

Arsenic 

As 

75 

74.96 

III  V 

5.7 

.  .  . 

<449 

sublimes 

Barium 

Ba 

137 

137.37 

II 

3.8 

850 

950 

Bismuth 

Bi 

208 

208.0 

III  V 

9.7 

269 

1435 

Boron 

B 

11 

11.0 

III 

2.4 

infusible 

3500 

sublimes 

Bromine 

Br 

80 

79.92 

I 

3.1 

-7.3 

59 

Cadmium 

Cd 

112 

112.4 

II 

8.6 

321 

778 

about 

Calcium 

Ca 

40 

40.07 

II 

1.5 

805 

.  .   . 

amorphous 

Carbon 

C 

12 

12.005 

IV 

1.7-2.1 

infusible 

3500 

Chlorine 

Cl 

35.5 

35.46 

I 

2.49 

-  102 

-33.6 

Chromium 

Cr 

52 

52.0 

II  III  VI 

6.9 

1505 

2200 

Cobalt 

Co 

59 

58.97 

II 

8.7 

1490 

. 

Copper 

Cu 

63.6 

63.57 

III 

8.9 

1083 

2310 

Fluorine 

F 

19 

19.0 

I 

1.31 

-223 

-  187 

Gold 

An 

197 

197.2 

I  III 

19.3 

1062 

2630 

Helium, 

He 

4 

4  00 

0  14 

960 

9fifi  ^ 

Hydrogen 

H 

1 

3.008 

I 

U.  IT: 

0.07 

-^  £\ju 

-259 

—  ^Oo.  O 

-252 

Iodine 

I 

127 

126  92 

I 

4.9 

114 

184 

Iron 

Fe 

56 

55.84 

II  III 

7.9 

1530 

2450 

Lead 

Pb 

207 

207.2 

II  IV 

11.3 

327 

1525 

234 


PHYSICAL   CONSTANTS 


235 


Kl.EMF.NT 

SYMBOL 

ATOMIC  WEIGHTS 

VALENCE 

SPECIFIC  GRAVITY 

MELTING 
POINT 

BOILING 
POINT 

Approx- 
imate 

Exact 
O—  16 

Water  ~1 

Air  =  1 

°<\ 

°0. 

Lithium 

Li 

7 

6.94 

I 

0.03 

•186 

<1400 

Magnesium 

M.u 

24 

24.32 

II 

1.7 

650 

1120 

Manganese  1  Mn 

55 

54.93 

II  IV 

7.4 

1225 

1900 

Mercury           Hg 

200 

200.6 

I  II 

13  6 

-38.8 

357  > 

Nickel             Ni 

58.7 

58.68 

II 

8.7 

1450 

( 

Nitrogen 

N 

14 

14.01 

IIIV 

0.97 

-213 

-195 

Oxygen 

O 

16 

16.00 

II 

1.10 

<-227 

-183 

white 

wh 

ite 

Phosphorus 

P 

31 

31.04 

IIIV 

1.8 

44.1 

290 

Platinum 

Pt 

195 

195.2 

IV 

21.2 

1753 

.  .  . 

Potassium 

K 

39 

39.10 

I 

0.87 

62.5 

757 

Silicon 

Si 

28 

28.3 

IV 

2.4 

1450 

3500 

Silver 

Ag 

108 

107.88 

I  , 

10.6 

961 

1955 

Sodium 

Na 

23 

23.0 

I 

0.97 

97.6 

877 

Strontium 

Sr 

87 

87.63 

II 

2.5 

900 

.  .  . 

rhombic 

Sulphur 

S 

32 

32.06 

II  IV  VI 

2.0 

114.5 

444.6 

14*10 

Tin 

Sn 

119 

118.7 

IIIV 

7.3 

232 

J.^Ov/— 

1600 

Zinc 

Zn 

65 

65.38 

II 

7.1 

419 

918 

236 


APPENDIX 


11 


QUIZ 

CO    CO    I-H    CO    CO      |     (-' 

CO    CO    HH    HH    CO    HH    PH 

IOAUS 

CO    ^    HH    CO    ^    —i  *    1 

^   CC   HH   HH   PH   ^   CO 

rampog 

CO    CO    CO    CO    CO    CO    CO 

CO    CO    CO    CO    CO    CO    CO 

uraiannoj 

CO    CO    CO    CO    CO    CO    CO 

CO    CO    CO    CO    CO    CO    CO 

pnpMi 

CO     CO     HH        |      CO        |      HH 

CO     CO     HH     HH     CO     HH     HH 

(++§H)  ouno,8M 

CO   CO   HH    CO   CO   PH   HH 

HH     CO    HH     HH     CO     ^        | 

f  Q    \ 

v+sHJ  snojnojaj\[ 

ereutfinw 

CO    CO    HH        |      CO        |      HH 

CO   CO   HH   PH   CO   HH     | 

mmsauSfeH 

CO    CO    HH    CO    CO    CO    H-I 

CO    CO    HH    HH    CO    CO    PH 

03     c3 

p^ai 

(+++9^1)  okudk! 

!     CO      |       |     CO      |     HH 

CO     HH     HH     CO        |         | 

(4-1.0  jj)  snojjaj 

CO     CO     HH         |       CO        |      HH 

CO   CO   HH    HH   CO    PH    PH 

joddoj 

CO    CO    HH    CO    CO    HH     HH 

•        CO     HH     HH     CO     ^     CO 

^qoD 

CO     CO    HH     CO     CO     HH     HH 

CO     CO     HH     HH     CO     HH     HH 

ranp^3 

co  co  HH  co  co  HH  PH 

CO    CO    PH    HH    PH    PH    PH 

nmjmpB3 

CC'CO    HH    CO    CO      |     HH 

CO     CO     HH     HH     CO     ^    CO 

i^Tinisig 

uinii'Bg; 

CO    CO    HH    CO    CO    HH    CO 

PH   CO   CO    HH   3   CO   HH 

snoiugsjy 

CO      |       |     CO      |     CO 

PH    |   M     15 

iuomnuy 

PH      |       |     PH      |     PH 

PH     1    -      1      1    5 

nmraoraray 

CO    i/}   CO    CO    CO    CO    CO 

CO    CO      |     CO    CO    CO    CO 

ranuicun^y 

CO    /}      |     CO    CO      |     HH 

O)    CO    M    HH    CO       |        | 

<D                                <D 

<1  W  O  O  O  8  W 

I  infill 

1  £  B  J  "3  3  3 

M  fc  O  PH  CO  co  co 

APPENDIX  237 

III.     GENERAL   RULES  FOR    SOLUBILITY 

Certain  generalizations  can  be  made  concerning  compounds  shown  in  the 
table  on  the  opposite  page.  The  exceptions  to  these  generalizations  are  few 
and  unimportant  for  the  beginner. 

1.  All  sodium,  potassium,  and  ammonium  compounds  are  soluble  in  water. 

2.  All  nitrates,  chlorates,  and  acetates  are  soluble  in  water. 

3.  All  chlorides  are  soluble,  except  those  of  silver,  mercury  (mercurous), 
and  lead  (lead  slightly  soluble). 

4.  All  sulphates  arc  soluble,  except  those  of  barium,  lead,  and  calcium 
(calcium  slightly  soluble).     The  silver  and  the  mercurous  sulphates  are  only 
moderately  soluble. 

5.  All  carbonates  are  insoluble,  except  those  of  sodium,  potassium,  and  am- 
monium. 

6.  All  oxides  and  hydroxides  are  insoluble,  except  those  of  ammonium, 
sodium,  potassium,  and  barium ;  calcium  hydroxide  is  slightly  soluble. 

IV.    VOLATILITY   OF   COMPOUNDS   THAT   MAY    RESULT 
FROM   DOUBLE  DECOMPOSITIONS 

1.  Compounds  volatile  at  ordinary  temperatures  : 

HC1    HBr     HF     H2S 

2.  Compounds  decomposing  at  ordinary  temperatures  yielding  volatile 
products : 

H2C03  (H20  +  CO,) 
H2S03  (H00  +  S()2) 
NH4OH  (H20  +  NH3) 

3.  Compounds  volatile  at  varying  temperatures  below  338°  (boiling-point 
of  sulphuric  acid)  : 

BOILING-POINT  BOILING-POINT 

H2O,  100°      HNO3,  86° 

HC1  (aqueous  solution),  110°      HXO3  (aqueous  solution),  120° 

HBr  (aqueous  solution),  126°      HC2H3O.,,  118° 

V.    APPROXIMATE  WEIGHT    OF   ONE  LITER   OF   COMMON 
GASES  UNDER  STANDARD  CONDITIONS 

Acetylene,  1.17  grams  Hydrogen  sulphide,  1.53  grama 

Ammonia,  0.77  "  Marsh  gas,  0.72  " 

Carbon  dioxide,  1.98  "  Nitrogen,  1.26  " 

Carbon  monoxide,  1.26  "  Nitric  oxide,  1.35  " 

Chlorine,  3.20  "  Nitrous  oxide,  1.98  " 

Hydrogen  chloride,  1.64  "  Oxygen,  1.43  " 

Hydrogen,  0.09  "  Sulphur  dioxide,  2.88  " 


238  APPENDIX 

VI.     THE  METRIC   SYSTEM   AND   ITS   EQUIVALENTS 

A.    Fundamental  Units 

The  International  Standard  Meier  is  the  distance  between  two 
lines,  at  0°  Centigrade,  on  a  platinum-iridium  bar  deposited  at  the 
International  Bureau  of  Weights  and  Measures  near  Paris,  France. 

MEASURES   OF   LENGTH 

10  millimeters  (mm.)  —  1  centimeter  (cm.) 
10  centimeters  =  1  decimeter  (dm.) 

10  decimeters  =  1  meter  (m.) 

The  International  Standard  Kilogram  is  the  weight  of  a  mass  of 
platinum-iridium  deposited  at  the  International  Bureau  of  Weights 
and  Measures. 

The  liter  is  equal  to  a  cubic  decimeter  and  it  is  measured  by  the 
quantity  of  distilled  water  which,  at  its  maximum  density  (4°  Centi- 
grade), will  counterpoise  the  standard  kilogram. 

Since  a  liter  contains  1000  cubic  centimeters,  one  cubic  centimeter 
of  water,  at  4°  Centigrade,  weighs  1  gram. 

B.    Important  Metric  Relations 


MEASURE 

RELATION 

Linear 

millimeter 
centimeter 

decimeter 

0.001  meter 
0.01    meter 
0.1      meter 

Capacity 

cubic  centimeter  = 

0.001  liter 

Weight 

milligram 
centigram 
decigram 

0.001  gram 
0.01    gram 
0.1      gram 

kilogram 

1000   grams 

WEIGHTS  AND  MEASURES 


239 


C.     Comparison  of  Metric  with  other  Weights  and  Measures 


METRIC  UNIT 

EQUIVALENT 

MEASURE 

Approximate 

Exact 

Meter 

• 

39.37         inches 

U.S.  Linear 

Centimeter 

0.4    inch 

0.3937      inch 

U.S.  Linear 

Liter 

1.06  quarts 

1.05668  quarts 

U..S.  Liquid 

Kilogram 

2.2    pounds 

2.20462  pounds 

U.S.  Avoirdupois 

Gram 

15.4    grains 

15.43235  grains 

U.S.  Avoirdupois 

UNIT 

U.S.  MEASURE 

EQUIVALENT 

Approximate 

Exact 

Yard 

Linear 

0.9    meter 

0.914402  meter 

Inch 

Linear 

2.5    centimeters 

2.54001     centimeters 

Gallon 

Liquid 

3.8    liters 

3.78543     liters 

Quart 

Liquid 

0.95  liter 

0.94636     liter 

Fluid  ounce 

Liquid 

29.6    c.c. 

29.574         c.c. 

Pound 

Avoirdupois 

0.45  kilogram 

0.45359     kilogram 

Pound 

Avoirdupois 

453.6    grams 

453.59           grams 

Ounce 

Avoirdupois 

28  3    grams 

28.3495      grams 

Grain 

Avoirdupois 

0.06  gram 

0.0648       gram 

240 


APPENDIX 


VII.     PRESSURE   OF    WATER  VAPOR,  OR    AQUEOUS  TENSION 

(In  Millimeters  of  Mercury) 


TEMPERATURE 

PRESSURE 

TEMPERATURE 

PRESSURE 

0.0°  C. 

4.6  mm. 

21.5°  C. 

19.1  mm. 

5 

6.5 

22 

19.7 

10 

9.2 

22.5 

20.3 

10.5 

9.5 

23 

20.9 

11 

9.8 

23.5 

21.5 

11.5 

10.1 

24 

22.2 

12 

10.5 

24.5 

22.9 

12.5 

10.8 

25 

23.5 

13 

11.2 

25.5 

24.3 

13.5 

11.6 

26 

25.0 

14 

11.9 

26.5 

25.7 

14.5 

12.3 

27 

26.5 

15 

12.7    . 

27.5 

27.3 

15.5 

13.1 

28 

28.1 

16 

13.6 

28.5 

28.9 

16.5 

14.0 

29 

29.8 

17 

14.4 

29.5 

30.7 

17.5 

14.9 

30 

31.6 

18 

15.4 

40 

55.0 

18.5 

15.9 

50 

92.2 

19 

16.4 

60 

149.2 

19.5 

16.9 

70 

233.8 

20 

17.4 

80 

355.5 

20.5 

17.9 

90 

526.0 

21 

18.5 

100 

760.0 

LIST  OF  SUPPLIES 

THE  following  list  is  an  estimate  of  the  material  advisable  to 
purchase  for  a  class  of  ten  pupils,  provided  each  student  per- 
forms all  of  the  experiments  described.  It  names  a  generous 
supply  of  apparatus  and  chemicals,  allowing  for  a  reasonable 
amount  of  breakage. 

In  case  of  somewhat  expensive  apparatus  it  has  been  assumed 
that  two  pupils  will  use  one  piece  of  apparatus.  Provision  has 
been  made  for  schools  not  having  laboratories  equipped  for  the 
use  of  the  electric  current. 

In  many  schools  it  is  practicable  to  arrange  the  laboratory 
work  so  that  all  of  the  members  of  the  class  do  not  perform  a 
certain  experiment  at  the  same  time.  In  such  cases,  the  num- 
ber of  expensive  pieces  of  apparatus  required  may  be  less  than 
that  mentioned  in  the  list. 

An  asterisk  follows  certain  items  on  the  list.  Such  articles 
are  relatively  less  necessary,  as  they  are  usually  needed  for  only 
a  single  experiment. 

GENERAL   APPARATUS 

5  pieces  apparatus,  electrolytic.* 
Form  shown  in  Fig.  10. 

1  apparatus,  electrolytic,  carbon  electrodes.* 
Form  shown  in  Fig.  24. 

1  doz.  sheets  asbestos,  thin  (baking-sheet).* 
10  squares  asbestos,  6"  x  6". 

2  balances,  platform,  with  weights  for  weighing  from  1000  grams 

to  0.1  gram. 
10  balances,  horn  pan,  7^-"  beam,  with  weights  for  weighing  from 

100  grams  to  10.01  gram. 
1  barometer. 

241 


242  APPENDIX 

10  blowpipes,  8". 
10  brushes,  test-tube. 
10  brushes,  small  tube. 
10  burners,  bunsen. 
20  candles,  birthday. 

10  capsules,  brass,  with  wire  holder  and  brass  ramrod,  for  holding 
sodium  below  water.* 
These  can  be  obtained  from  Eimer  and  Amend,  New  York. 

15  cells,  dry  battery.* 

2  pkg.  cigar  lighters,  wood. 

20  clamps,  iron,  small ;  for  test  tubes,  burettes,  etc. 
10  clamps,  iron,  large  ;  for  Liebig  condensers. 

1  gross  corks,  assorted  sizes,  long. 

1  set  cork  borers,  6  in  set. 
12  crucibles,  porcelain,  with  lids,  ft  00. 
25  cups,  agate  ware,  1  pt.  (or  stew  pans).* 
12  dishes,  porcelain,  evaporating,  ft  0.     . 
10  dishes,  porcelain,  evaporating,  ft  1. 
10  droppers,  medicine. 
10  files,  triangular,  5". 
10  pr.  forceps,  iron,  4". 
10  squares  gauze,  iron  wire  with  asbestos  center,  5"  x  5''. 

1  glass  cutter. 

10  holders,  test  tube. 

5  lamps,  incandescent,  100  watt.* 

5  magnifiers,  Coddington  lens,  or  other  make. 

5  mortars,  with  pestle,  31". 
12  pans,  enamel,  shallow,  1  qt. 
10  pans,  iron,  5  in.,  shallow  form,  "  sand  bath." 
10  pkg.  paper,  filter,  qualitative,  good  quality,  4". 

2  sheets  paper,  black,  glazed. 

10  pinch-cocks,  Mohr's,  medium.* 

10  ft.  platinum  wire,  #25.* 

10  racks,  test  tube,  for  12  tubes. 

5  shears,  6".* 

5  sheets  sandpaper,  ft  1. 

5  spatulas,  horn,  6". 


LIST  OF  SUPPLIES  243 

10  spoons,  deflagration,  diam.  of  bowl  1  cm. 
10  stands,  iron,  ring,  3  rings. 

2  Ib.  stoppers,  rubber,  assorted  sizes,  #  0-5,  one-  and  two-hole. 

1  pkg.  tapers,  wax. 
10  thermometers,  chemical,  0°-250°  C. 

1  spool  thread,  #  50,  cotton. 

10  tripods,  iron,  for  supporting  dishes  over  burner,  ring  4"  in  diam. 
10  triangles,  pipestem,  size  to  support  #  00  porcelain  crucible. 
10  troughs,  pneumatic. 
50  ft.  tubing,  rubber,  inside  diam.  -f^". 
20  ft.  tubing,  rubber,  inside  diam.  f ". 
5  yard-sticks.* 

GLASSWARE 

24  beakers,  100  cc. 
36  beakers,  150  cc. 
36  beakers,  250  cc. 
12  beakers,  500  cc. 
100  bottles,  reagent,  4  oz. 
30  bottles,  wide  mouth,  4  oz. 

40  bottles,  wide  mouth,  6  oz.,  with  two-hole  rubber  stoppers  to  fit. 
10  bottles,  wide  mouth,  8  oz.,  with  two-hole  rubber  stoppers  to  fit. 

2  bottles,  wide  mouth,  16  oz.,  with  two-hole  rubber  stoppers  to  fit. 
10  bottles,  acid,  2|  liters. 

20  burettes,  50  cc.,  graduated  to  ^  cc.,  complete.* 

10  condensers,  Liebig,  15".* 

12  flasks,  distilling,  250  cc.* 

12  flasks,  Florence,  50  cc. 

12  flasks,  Florence,  100  cc.,  with  one-  and  two-hole  rubber  stoppers 

to  fit. 

12  flasks,  Florence,  250  cc.,  with  two-hole  rubber  stoppers  to  fit. 
12  flasks,  Erlenmeyer,  50  cc. 

12  flasks,  Erlenmeyer,  250  cc.,  with  two-hole  rubber  stoppers  to  fit. 
24  funnels,  accurate  60°,  2|". 
10  graduates,  50  cc.,  graduation  marks  to  1  cc. 
2  graduates,  1000  cc.,  graduation  marks  to  10  cc. 
10  jars,  battery,  about  4"  x  5". 
10  jars,  hydrometer,  12"  x  2". 


244  APPENDIX 

5  pipettes,  10  cc.* 
40  plates,  glass,  2J"  x  2£". 
10  plates,  glass,  4"  x  4". 

40  plates,  cobalt  glass,  for  flame  tests,  3"  x  2".* 
15  retorts,  tubulated,  with  ground-glass  stopper,  4  oz.* 

1  Ib.  rods,  3  mm.  diameter. 

10  tubes,  gas  measuring,  50  cc.,  graduated  to  TL  cc. 

15  tubes,  test,  hard  glass,  for  ignition,  6"  x  f  ",  with  one-hole  cork 

stoppers  to  fit. 
12  tubes,  test,  side  arm,  6".* 
15  doz.  tubes,  test,  soft  glass,  medium  walls,  for  heating,  6"  X  |". 

2  doz.  tubes,  test,  soft  glass,  medium  walls,  for  heating,  4"  x  V- 
15  tubes,  thistle,  10",  stem  T3g- "  in  diameter. 

12  tubes,  U,  6",  with  two-hole  rubber  stoppers  to  fit. 
12  tubes,  U,  4",  with  one-hole  rubber  stoppers  to  fit.* 
2  Ib.  tubing,  soft  glass,  medium  walls  for  bending,  outside  diame- 
ter 4  mm. 

24  watch  glasses,  diameter  2-|". 
40  watch  glasses,  Syracuse  form,  diameter  3".* 

CHEMICALS   AND   OTHER   SUPPLIES 

1  Ib.  acid,  acetic,  30  % ,  c.  p. 

1  oz.  acid,  acetic,  glacial.* 

2  oz.  acid,  boric,  c.  p. 

1  oz.  acid,  citric,  c.  p. 
4  oz.  acid,  formic.* 

12  Ib.  acid,  hydrochloric,  c.  p.,  sp.  gr.  1.19. 
7  Ib.  acid,  nitric,  c.  p.,  sp.  gr.  1.42. 

2  gr.  acid,  picric.* 

1  Ib.  acid,  oxalic,  cryst.,  c.  p. 

1  oz.  acid,  salicylic.* 

9  Ib.  acid,  sulphuric,  c.  p.,  sp.  gr.  1.84. 

1  oz.  acid,  tannic,  c.  p. 
4  oz.  acid,  tartaric. 

2  qt.  alcohol,  ethyl,  95  %. 

I  pt.  alcohol,  methyl  (wood  alcohol).* 
4  oz.  alizarine,  paste,  25  %* 


LIST  OF  SUPPLIES  245 

1  oz.  alpha  naphthol.* 

8  oz.  aluminum  sulphate,  cryst. 

1  Ib.  ammonium  chloride,  c.  p. 

10  Ib.  ammonium  hydroxide,  c.  p.,  sp.  gr.  0.9. 
8  oz.  ammonium  nitrate,  cryst.,  c.  p. 

2  oz.  ammonium  oxalate,  cryst.,  c.  p.* 
4  oz.  ammonium  sulphate,  c.  p. 

1  oz.  antimony,  lumps  (powder,  if  necessary,  just  before  using).* 

1  Ib.  barium  chloride,  cryst.,  c.  p. 

4  oz.  barium  nitrate,  c.  p. 

2  oz.  benzol.* 

5  gr.  Biebricht  scarlet  (or  tartrazine,  or  acid  blue).* 
8  oz.  bleaching  powder. 

1  Ib.  boneblack. 

1  oz.  bromine.* 

1  oz,  cadmium  nitrate,  c.  p.* 

i  Ib.  calcite.* 

5  Ib.  calcium  carbonate,  marble  chips. 

1  Ib.  calcium  chloride,  granular,  for  drying  tubes. 

2  oz.  calcium  nitrate,  c.  p. 

2  Ib.  calcium  oxide,  good  quality  of  lime  in  tin  can. 
2  oz.  calcium  phosphate  (monocalcium).* 
5  Ib.  calcium  sulphate,  plaster  of  Paris,  fine. 
1  Ib.  carbon  disulphide. 
4  oz.  carbon  tetrachloride.* 
^  Ib.  chalk,  precipitated.* 
12  blocks  charcoal,  for  blowpiping. 
1  oz.  charcoal,  wood,  powdered. 

1  Ib.  chloroform.* 

2  oz.  chromium  sulphate,  c.  p.  (or  chrome  alum). 

^  yd.  cloth,  calico,  bleachable  color,  for  bleaching  with  chlorine. 

1  yd.  cloth,  cotton,  bleached,  fine  goods. 
£  yd.  cloth,  woolen.* 

2  yd.  cheesecloth. 

1  oz.  cobalt  nitrate,  cryst.,  c.p. 
10  grams  congo  red.* 
4  oz.  copper  foil,  y^/'  thick.* 


246  APPENDIX 

10  sq.  in.  copper  gauze,  80  meshes  to  inch.* 
2  Ib.  copper  rivets,  \" . 
\  Ib.  copper  sheet,  -£%'  thick. 
2  Ib.  copper  turnings,  clean,  fine. 
1  Ib.  spool  copper  wire,  ft  16. 
1  Ib.  spool  copper  wire,  ft  18. 
1  Ib.  spool  copper  wire,  ft  24. 
1  Ib.  spool  copper  wire,  ft  30. 
1  oz.  copper  oxide,  powdered,  c.  p. 
1  oz.  copper  oxide,  wire  form. 
1  oz.  copper  sulphate,  anhydrous. 
1  Ib.  copper  sulphate,  cryst.,  c.  p. 

1  oz.  cotton,  absorbent. 

2  Ib.  cotton  waste,  unbleached.* 

2  oz.  Fehling's  solution,  two  solutions  in  separate  bottles. 
10  grams  fuchsine.* 
8  oz.  glucose.* 
4  oz.  hydrochinone.* 
1  Ib.  hydrogen  peroxide. 

1  oz.  iodine,  resublimed.* 

10  oz.  iron  and  ammonium  citrate,  green  (ferric  ammonium  citrate) 
4  oz.  iron  chloride,  ferric,  c.  p. 

2  oz.  iron  filings,  fine,  clean. 

1  Ib.  iron  sulphate,  cryst.,  c.  p. 

4  oz.  iron  sulphide,  ferrous,  in  sticks,  for  H2S. 
1  Ib.  spool  iron  wire,  ft  16. 

1  Ib.  spool  iron  wire,  ft  25. 

2  oz.  lead  acetate.  ' 

1  Ib.  lead  nitrate,  c.  p. 

5  Ib.  lead  shot,  ft  10. 
i  oz.  lithium  nitrate. 
1  oz.  litmus  cubes. 

•J-  quire  each,  red  and  blue  litmus  paper. 

4  oz.  logwood,  ground.* 

1  oz.  magnesium,  powder.* 

1  oz.  magnesium,  ribbon. 

1  Ib.  magnesium  sulphate,  cryst. 


LIST  OF  SUPPLIES  247 

10  grams  malachite  green.* 

2  Ib.  manganese  dioxide,  fine,  granular,  free  from  carbon. 

4  oz.  manganese  dioxide,  c.  p.* 

1  oz.  mercuric  nitrate. 

8  oz.  mercuric  oxide,  red. 

1  oz.  mercurous  nitrate. 

1  pt.  molasses,  good  quality,  kettle-rendered.* 
24  sheets  paper,  unglazed. 
10  grams  phenolphthalein. 

%  oz.  phosphorus,  red. 

1  oz.  phosphorus,  yellow. 

1  Ib.  potassium  and  aluminum  sulphate,  alum. 

1  oz.  potassium  antimonyl  tartrate  (tartar  emetic).* 

4  oz.  potassium  acid  tartrate. 
10  oz.  potassium  bromide. 

1  Ib.  potassium  chlorate,  cryst.,  c.  p. 

2  oz.  potassium  chromate.* 

1  oz.  potassium  and  chromium  sulphate  (chrome  alum).* 
8  oz.  potassium  dichromate.* 

1  Ib.  potassium  ferricyanide. 

2  oz.  potassium  ferrocyanide. 

2  Ib.  potassium  hydroxide,  c.  p.,  by  alcohol. 

2  oz.  potassium  iodide,  c.  p. 

2  Ib.  potassium  nitrate,  cryst.,  c.  p. 

1  oz.  potassium  permanganate,  c.  p. 

1  oz.  potassium  oxalate.* 

8  oz.  potassium  sulphate,  c.  p. 

1  Ib.  salt,  rock.* 

4  oz.  silver  nitrate,  c.  p. 

1  oz.  soap,  castile,  powdered. 

2  oz.  sodium. 

4  oz.  sodium  acetate. 

2  oz.  sodium  aluminum  sulphate  (sodium  alum).* 

1  Ib.  sodium  bicarbonate,  baking  soda. 

4  oz.  sodium  bisulphite.* 

1  Ib.  sodium  carbonate,  cryst.,  washing  soda. 

8  oz.  sodium  carbonate,  pure,  dry. 


248  APPENDIX 

5  Ib.  sodium  chloride,  salt,  fine. 

2  oz.  sodium  chromate,  powdered.* 

1  Ib.  sodium  hydroxide,  c.  p.,  by  alcohol. 

1  oz.  sodium  iodide  (or  potassium  iodide).* 

1  Ib.  sodium  nitrate,  c.  p. 

2  oz.  sodium  peroxide. 

8  oz.  sodium  phosphate,  c.  p. 

2  oz.  sodium  phosphate  (monosodium).* 

2  Ib.  sodium  sulphate,  cryst. 

1  Ib.  sodium  sulphite,  pure,  dry.* 

2  Ib.  sodium  thiosulphate  ("  hypo  "). 
1  Ib.  sodium  tetraborate  (borax). 

1  Ib.  starch,  corn. 
1  Ib.  starch,  potato. 

1  oz.  strontium  nitrate,  c.  p. 

2  Ib.  sulphur,  roll. 

8  oz.  tin,  granulated. 

1  sheet  turmeric  paper. 

1  qt.  vinegar,  cider.* 

1  oz.  wool,  glass,  fine  Bohemian. 

1  pkg.  wool,  steel,  fine. 

8  oz.  yarn,  woolen,  white.* 

1  Ib.  zinc,  sheet. 

2  Ib.  zinc,  granulated  (mossy). 
2  oz.  zinc  dust.* 

1  oz.  zinc  nitrate. 
8  oz.  zinc  sulphate. 

A  very  few  articles,  such  as  flour,  yeast,  foods  for  testing,  and 
other  articles  of  common  household  use,  have  been  omitted  from 
the  above  list. 


' 


/.*}} 


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